How Bluetooth Car Stereos Work

If you hear the name Bluetooth, the first images that come to mind could be of half-concealed headsets. But a growing number of people imagine a whole lot more, including car stereos.

Bluetooth is a growing technological trend that many people use to varying extents. Some simply clip a headset on their ear to talk on a cell phone without the need to hold the actual phone. Others maximize Bluetooth's capabilities and have fully synchronized networks in their homes, offices and vehicles. And still some don't know much about Bluetooth at all. Here are the basics.

Bluetooth devices communicate wirelessly with each other through short-range radio waves that have a maximum reach of about 10 meters generally, or 30 feet, although some more high-powered devices have longer ranges. Unlike devices that require a direct line of sight like remote controls, Bluetooth-enabled products just need to be in the same area in order to communicate with each other.

The interactions between devices form a small network, commonly called a piconet or a personal area network (PAN). These mini-networks, typically comprising no more than eight electronic gadgets, communicate in interesting ways -- all the while guided by the Bluetooth connection protocols and standards that unify the exchanges.

The machines, controlled by one master device, detect each others' presence and pass around pertinent data to coordinate and facilitate their activities at the same time they're continually jumping between radio frequencies along a certain band. With this constant hopping and the use of low power signals, Bluetooth gadgets not only cut down on interference from other devices sharing the frequency band, they also help ensure any brief crossovers won't be an issue.

A variety of electronics can be part of a Bluetooth piconet, from cell phones to personal computers and printers to cameras. The growing list also includes home phones, headsets, entertainment systems, GPS navigators, MP3 players and more. Bluetooth technology is touted as being an inexpensive automated system that brings convenience, flexibility and efficiency to electronic network communication -- and the daily lives of its users.

Capabilities of a Bluetooth Car Stereo System

Bluetooth car stereos have lots of features, from hands-free calling to video displays.

Now that we've got a handle on Bluetooth 101, let's see what it can do in a stereo. Bluetooth car stereos are commonly integrated with Bluetooth-enabled cell phones, and when the two devices are within range of each other, they can communicate in a number of interesting ways. Depending on the particular models in use, it may be possible to make and receive calls without even pulling out your phone or pushing a single button. You can even hear the calls through the vehicle's speakers. Other models may require a few button-pushes, but usually with more ease than plodding through cell phone menus. You may also be able to view other information such as the phonebook, incoming calls and call status on the stereo panel. When the phone rings, the speakers will automatically turn down the volume on any music or movies that are playing while you chat on the phone and resume when the call is over.

Some Bluetooth car stereos can store your phone's entire address book and other contact information; others have built-in phones which copy all the information off your phone's SIM card and take over the functions for calling. Your cell phone is disconnected from the piconet, not only saving its battery power but also providing a stronger connection.

These innovations come almost as much out of necessity as convenience -- at least for people who can't stand being in the car without making a quick phone call. Many places now enforce laws limiting the use of cell phones while driving, and Bluetooth car stereos are one way to bridge the middle ground.

Besides augmenting your ability to connect with the outside world through phone calls, Bluetooth car stereos can also enhance the environment inside a vehicle. Transmitters can be used to stream music from iPods, MP3 players and satellite radio straight into the stereo without creating a mess of tangled cords. Some car stereos can display video on full-color LCD displays, although this usually isn't an option when the car is moving. If you have some passengers in the back who could use a movie to settle down, lots of Bluetooth-enabled car stereos also come with the hookups needed to turn your vehicle into a mobile entertainment center. Connections for other devices like GPS navigators and USB flash drives are among other common fixtures.

And with each passing year, the technology grows and evolves. Comparing Bluetooth-enabled car stereos to cassette-enabled car stereos already seems like a throwback to the Middle Ages, so who knows what the future has in store.

Buying a Bluetooth Car Stereo

Audi is one of several carmakers whose newer car models often come Bluetooth-enabled.

­Many new vehicles come with Bluetooth-enabled stereos straight from the factory, but you can also purchase specific or universal adapters if your car isn't one of them. The universal adapters are more likely to have limited functions, while the stereo-specific ones offer a broader range of features. Stereos that have Bluetooth built in tend to be the most advanced, as we read on the last page, often with full phone control, streaming music capabilities and more.

There are a couple of considerations you'll want to keep in mind, though. Some cars have stereos that are more challenging to substitute out than others. For example, if your vehicle has a climate control system or other key feature linked through the stereo, you might want to reconsider yanking it out. Those who are slightly less tech-savvy should also make sure the Bluetooth car stereo they have their eye on is one they can actually operate efficiently. Hands-free capabilities aren't much of a benefit if you spend all your time fiddling with the controls trying to make everything work properly.

On a similar note, it's also a good idea to thoroughly check the features on your Bluetooth car stereo to make sure it has all the functions you want. Nothing worse than taking an expensive new acquisition out for a test drive only to find it only gets half the job done. Although Bluetooth is a universal technology, there can be some hang-ups if you try using newer Bluetooth devices with older ones, so it's smart to verify everything in your electronics landscape will get along before making any purchases. Security might also be an issue. Many models feature some modicum of theft protection, whether the ability to remove the face of the stereo or flip it around to make it more low key.

One concern with using Bluetooth technology is the possibility of being hacked. If you'll recall from the first page of this article, Bluetooth operates on radio waves, and hackers can use this to their advantage to interfere remotely in a number of different ways. They can potentially steal passwords, and they can also reportedly communicate with a passing Bluetooth network.

This particular hack, known as the Car Whisperer, allows someone to listen in to a Bluetooth network set in a vehicle -- whether a phone call or a simple conversation between driver and passenger -- and even participate in that conversation if they choose. A nonprofit organization called the Trifinite Group tested the Car Whisperer phenomenon, and they proved that unprotected devices are at risk should a hacker be in the vicinity -- although with some simple equipment, the vicinity can cover a much larger range than Bluetooth networks traditionally encompass. Plus, if the hacker was following his or her unknowing target in a vehicle, the eavesdropping could become even more serious. Strong password encryption and other security measures are steps manufacturers and users can take to help diffuse the threat.

Are RFID ignition systems secure?

An RFID-equipped key could help throw off the thieves -- or not.

In 1997, Ford Motor Co. equipped the Mustang with one of the first RFID ignition immobilizers in the U.S. car industry. Theft levels for the Mustang immediately dropped 70 percent from just two years prior [source: Stone]. The results were stunning, and pretty much every other carmaker followed suit.

Today, the RFID (radio frequency identification) industry claims a 90 percent reduction in theft rates for car models equipped with RFID starters, immobilizers and entry systems [source: Vamosi]. Both automakers and insurance companies have full faith in the devices, even going so far as to label them unbeatable. And certainly, the technology is an impressive display of security innovation.

RFID relies on radio-frequency signals to create a system that, for the first several years it was in use, was indeed uncrackable. In the 1990s, many a car thief was thwarted by the rather brilliant addition of RFID immobilizers to regular old physical keys. An RFID immobilizer is a chip embedded in the top part of an ignition key. This chip sends out an encrypted string of radio-frequency signals, basically a particular number of impulses broadcast on various radio frequencies to create a specific code, when the driver inserts it into the ignition-key slot. Without this code, the car either won't start or won't activate the fuel pump. So even if someone hotwires the car or copies an ignition key, the ignition isn't going to work because it hasn't received the proper radio-frequency code.

If you have a car that comes with a special "valet key," the immobilizer probably shuts down the fuel pump if the car is started without the code. This means the car is going to run only on whatever fuel is left in the fuel line, which will only get it a couple of blocks. Thus the valet key -- valet parkers only have to drive a car very short distances. If they try to drive off with your car, they won't get very far. Neither will any other potential car thief.

­Early RFID systems, both keyless entry (the key fob device with the button you press to unlock the car) and vehicle immobilizers, used 32-bit encryption. That means they sent a code of 32 impulses. With 32 bits in the code, there are billions of possible combinations [source: Stone]. In newer schemes, including remote starters that let you start a car with the push of a button, the codes have 40 bits, which increases the possibilities. With so many possible codes, the system seems unbeatable.

RFID Car Systems: Radio Protection

Radio-frequency identification tags use similar technology to RFIDs used in cars.

­Cars with RFID security do have lower theft rates, and it makes sense. This type of system makes getting in and driving off a lot more complicated.

Keyless entry and immobilizer systems work in pretty much the same way. Let's say you have a keyless-entry fob. It's a standard radio-transponder setup: Inside is a circuit board, a radio transmitter, a battery and an antenna. When you get near your car, perhaps 5 feet to 10 feet (a few meters) away, you press the button to unlock your doors. The RFID chip in the fob sends out a code of 40 impulses broadcast on different frequencies. The corresponding RFID chip in the car receives this code and accesses the car's software to find out if the code is the right one. If it is, the doors unlock.

This is called an active RFID system, since pushing the button actively sends out the code, instead of receiving it. The immobilizer chips in ignition keys are also active. Keyless ignition, on the other hand, is a passive RFID system. Instead of the ignition chip sending out the code, the car sends out the code and the ignition chip receives it. Ignition systems have no battery (or a different kind), and they have a lower-power antenna, so they won't broadcast as far. It's an additional security measure.

On its face, the system seems impenetrable: There are billions of possible sequences, and brute force will no longer get the car moving. Add in rolling codes, which are becoming more common -- a system in which the expected sequence changes slightly every time you push the button -- and the options get closer to a trillion. But as with any security system, it's only impenetrable until thieves figure out a way around it. Look at safes and burglar alarms; you've got to update those frequently in order to stay ahead of the robbers. Car RFID systems are no different.

RFID hacking is the most high-tech approach to car theft yet. Using hardware that grabs radio frequency signals out of the air, and software that decrypts it, thieves with time on their hands can steal an RFID-equipped car. In 2005, researchers at Johns Hopkins University in Maryland demonstrated how.

RFID Security: Hacking In

iStockphoto/jibelien
A thief with a laptop and a microreader can capture the transmissions sent out by an RFID.

­The fact is, people steal cars equipped with RFID security. It's especially common in Europe, where RFID has been used in cars for longer than in the United States. To prove the weaknesses of the system, researchers at Johns Hopkins went about breaking in. What they found was startling.

If you equip a laptop computer with a microreader, a device that can capture radio signals, you can capture the transmissions sent out by an RFID immobilizer key. Positioned within a few feet of the RFID transponder -- say, sitting next to the car owner in a restaurant -- the laptop sends out signals that activate the chip. When the key begins broadcasting, the reader grabs the code, and the computer begins decrypting it. Within 20 minutes, you've got the code that'll tell the car to start. (Once you have a good database of codes stored in your laptop, the time gets much shorter.) Pair that code with a copy of the physical key or a hotwire job, and you're on your way. In the case of the passive ignition system, the process is similar, but you need only stand next to the car, not the person carrying the key.

In cars that have RFID entry and ignition, it's an all-in-one process. Break the codes, and you can not only unlock the doors, but also start the car and drive away. According to some security experts, this is the problem with the system. RFID is a really great addition to a car's physical security system, but on its own, it allows for complete access with just a single act of decryption. For a thief with good equipment, it's a snap.

This is where the RFID, insurance and car industries object to the portrayal of RFID systems as faulty. Sure, the Johns Hopkins researchers could break it. They have money and hardware. Car thieves would never take the time or spend the money to break an encrypted code.

But with the payoff of tens of thousands of dollars for a high-end car, thieves have decided to give it a whirl. And whereas locksmiths weren't allowed to copy RFID-equipped keys at first, annoyance on the part of car owners who lost their keys led to a loosening of the rule. Now, both locksmiths and regular consumers can buy kits that can capture and clone an RFID code. The result is that people are losing their RFID-secured cars, and insurance companies call the owners' claims fraudulent because RFID security is uncrackable. The owners must be lying.

There are a few possible solutions to this problem that don't involve scrapping RFID. The Johns Hopkins scientists propose several ways to better secure the system: First, RFID makers should switch from 40-bit to 128-bit encryption; owners should wrap their fob in tinfoil when not using them, to help block fraudulent signals from activating transmission; and most important, carmakers should use RFID technology as an additional security measure, not the sole one.

As with any other security system, the advice is simple: Layer up. Don't rely on any single protection method. Instead, use several different types of security in order to make it as complicated as possible to bypass.

How Anti-sleep Alarms Work

Falling asleep at the wheel can be dangerous for everyone on the road.

Everyone knows about the alarms that abruptly wake us from our slumbers each morning, but have you heard of alarms that can keep us awake while we're driving? Anti-sleep alarms do more than simply startle and annoy drivers -- they can save them from fender benders or worse by alerting them if they start to nod off behind the wheel.

There are two types of anti-sleep alarms. The first type of alarm is built right into the car and uses sensors, cameras and other high-tech tricks to discern a driver's fatigue and correct the problem accordingly. The second type fits over the driver's ear and sounds an alert when the driver starts to fall asleep. While the in-car alarm systems are a recently developed feature that can add thousands of dollars to a car's sticker price, the over-the-ear alarm is both cheap and readily available. Drivers can find these for $10 to $20 under brand names like Nap Zapper, No Nap, and Doze Alert.

­The names might sound funny, but the need for anti-sleep alarms is no joke. A poll conducted by the National Sleep Foundation showed that 60 percent of Americans have driven while feeling sleepy, and 37 percent admit to falling asleep at the wheel in the past year. In fact, sleepy driving can be deadly: The National Highway Traffic Safety Administration (NHTSA) reports that drowsy driving causes more than 100,000 car crashes -- and kills more than 1,500 people -- each year. While the safest course of action is to get a good night's sleep or to take a nap before driving, an anti-sleep alarm could come in handy on a late-night drive.

Keep reading to find out how these gadgets see you when you're sleeping and know when you're awake

Sensing Driver Sleepiness

An anti-sleep alarm would have already awakened this tired driver.

Let's start with the simplest anti-sleep alarm system, the over-the-ear gadget. This lightweight plastic device has an arm that slips over one ear, like some telephone earpieces or portable headphones do. Once it's on, a sensor inside the case measures the angle from a perpendicular perspective. If the driver is looking straight ahead -- as he or she should -- the alarm measures the angle at zero degrees.

If you've ever fallen asleep on a subway train or in your high school algebra class, you know that your head tends to fall forward as you doze off. You also know that you may stay asleep for a few seconds or a couple of minutes before your head jerks upright and you're awake again. It's annoying on the bus commute home; it's downright dangerous when driving a car. The anti-sleep alarm looks for any indication that the driver's head is tipping forward: When the earpiece senses that the angle has increased from zero to, say, 15 or 30 degrees, it sounds an alarm. Most manufacturers stress that the sound is loud and irritating enough to wake the driver, but not so loud or sudden that he wakes up with a start and yanks on the wheel or steps harder on the gas.

You can easily adjust the angle that triggers the alarm. If you know you can sleep with your head almost upright, you can set your earpiece to a smaller angle. If the alarm goes off every time you bop your head along with the tunes on your radio, then you should set your triggering angle to 30 degrees or more.

While these alarms work to help keep drivers awake, some high-end manufacturers are adding sleep sensors to their cars right at the factory. A few notable systems:

• Mercedes-Benz Attention Assist uses the car's engine control unit to monitor changes in steering and other driving habits and alerts the driver accordingly.
• Lexus placed a camera in the dashboard that tracks the driver's face, rather than the vehicle's behavior, and alerts the driver if his or her movements seem to indicate sleep.
• Volvo's Driver Alert Control is a lane-departure system that monitors and corrects the vehicle's position on the road, then alerts the driver if it detects any drifting between lanes.
• Saab uses two cameras in the cockpit to monitor the driver's eye movement and alerts the driver with a text message in the dash, followed by a stern audio message if he or she still seems sleepy.

In-car systems can be expensive, especially those that involve in-dash cameras to monitor drivers instead of sensors that are already in place. Read on to find out who can benefit from an anti-sleep alarm, no matter what the cost.

Who Needs an Anti-Sleep Alarm?

Are You a Drowsy Driver? The National Sleep Foundation has a few tips to share so you can tell if you're too sleepy to drive: Difficulty focusing, frequent blinking or heavy eyelids Daydreaming, or wandering and disconnected thoughts Trouble remembering the last few miles driven Missing exits or traffic signs Yawning repeatedly or rubbing your eyes Trouble keeping your head up Drifting from your lane, tailgating or hitting a shoulder rumble strip Feeling restless and irritable

D­rivers are the obvious target market for anti-sleep alarms. Truck drivers with tight schedules often find themselves hauling freight overnight. An alarm worn over the ear and a thermos of coffee could be enough to keep drivers alert without resorting to pharmaceuticals. Even the casual spring break road tripper could use a sleep alarm.

Over-the-ear alarms have uses beyond the driver's seat. A student cramming through the night could skip the usual chemical ways to stay awake and slip an alarm over his or her ear instead. Night security guards, especially those who work in stationary posts and gate houses, could also make use of this simple technology.

While these alarms can keep tired eyes open and brains alert enough to study, driving while sleepy is dangerous. Having a sleep alarm either built into in the car or worn on the ear may give tired drivers a false sense of security. This danger led the Australian state of Victoria to ban the devices in 2007 pending further safety testing.

Anti-sleep alarms would help travelers who'd rather hit the road than the hay, but the best and safest remedy for a driver's drooping eyelids is to stop and take a nap.