This type of system is triggered by either a key fob attached to your keychain, or by a device built into the plastic grip on the key itself. One button unlocks your car; the other one locks it. A third button opens the tailgate or trunk, and a fourth button, usually red, activates and deactivates a pulsing series of horn blasts to alter passersby if your safety is threatened. If your car is equipped with a car alarm, the fob will also have buttons for activating and deactivating the vehicle security system. Many keyless entry remotes will also close your sunroof and roll up the windows you left open when you send the signal to lock the doors.

Your keyless entry remote fob is a miniature radio transmitter that acts as an electronic key to your vehicle’s doors. The signal is much like the ones used in radio-controlled toys. The fob also contains a circuit board, an antenna, and a battery. Pushing one of the buttons on the fob activates the transmitter, which sends a signal to the receiving unit inside your car. The receiver is tuned to the same frequency as the transmitter. It looks for a signal that matches the one it’s been programmed to receive. If it gets one, it unlocks your doors.

An automotive keyless entry system performs all the functions of a normal car key, but without touching the vehicle. You can lock and unlock your power door locks from up to 50 feet away (depending on how fresh the battery is), and even from indoors. Just like a normal key, locking your keyless remote fob inside your vehicle is a problem if you don’t have a spare.

So much for how it works. But is it secure? To understand the answer to this question, you need to know the history behind this type of system.

The precursor of keyless entry locks was the good old automatic garage door opener that first came into wide use in the 1950s. The transmitters in these units were so simple that they all sent out the same signal. It didn’t take long for thieves to figure out that they could open all the garage doors on one street with just one transmitter.

The 1970s saw the advent of DIP switches in garage door openers. These were an eight-switch transmitter that you programmed with a keypad and matched the code up with the receiver inside your opener. This was improvement over the original design, but eight switches only had 256 possible combinations—enough to discourage opportunistic theft, but no match for professional thieves, and not secure enough to use in automotive applications.

Modern keyless remotes began in the 1990s with the introduction of a small computer chip in the transmitter unit that can generate literally billions of possible codes. At this point, automobile keyless entry became standard equipment on all but the cheapest cars. Car thieves responded by using laptop computers with wireless cards to pick up the signal from a car owner’s key fob. They would store the signal and track the owner to where he left his vehicle, then stole it.

The vehicle security industry’s response was the 40-bit rolling code, also called a hopping code. This type of keyless entry lock generates a new code sequence each time you use your key fob to open or close your car door. The receiver chip inside your car is synchronized with the transmitter on the key fob to accept the new code as the fob generates it. The thief who picks up the code sequence you use to open your car will find that it doesn’t it work if he follows you to a parking lot and tries to use it after you’ve left your vehicle.

One problem with rolling codes is that if you get out of range of your car and then press the button on your key fob, the keyless entry chip in your car won’t know what the new hopping code sequence is. In that case, the receiver chip is programmed to predict the next 256 hopping codes that your key fob will generate and accept any of them. So unless you accidentally push the button 257 times, your keyless remote will still work when you push the button.

The same technology found on these systems is also used on radiofrequency ignition devices (RFIDs). This is a car theft prevention technology which locks out your ignition system until you send it a signal to unlock by either pressing a button on the key fob, or inserting your key in the ignition.

Of course, a commercial car security system is a lot more than a switch and a siren. Their parts include:

All kinds of sensors, including motion detectors, pressure sensing devices, and switches

A noisemaking device such as a siren, that wails with different sounds so you an identify your vehicle if it goes off

A signal receiving device so you can set and deactivate your car alarm from the transmitter on your keychain

A separate battery to keep the alarm working if the car’s battery quits

Most importantly, a electronic control board to keep all the other parts working together

The electronic control board is called the “brain.” It’s really just a miniature computer that operates the switches on the alarm’s outputs (like the siren, horn, or headlights), in response to certain inputs, like your vehicle door opening, or window glass breaking, or someone touching the outside. How many inputs the brain will respond to by triggering the alarms depends on the complexity and price of your alarm system. The brain also has a small radio signal receiving unit that arms and disarms the alarm system in response to a signal from your key fob.

Although it’s possible for the brain to get its power from the car’s primary battery, a good alarm system will have its own smaller battery hidden away so thieves can’t disable the alarm by disconnecting the power. A really smart car alarm will activate the siren and lights when the main battery current is cut, since this is usually a sign that someone is tampering with your vehicle.

Door sensors are the basic input device on all car alarms. When the system is armed, and someone opens the hood, a door, or the trunk, the brain activates the noisemakers and lights. Most alarms use the existing switches that also activate the dome light and trunk light

Shock sensors are the next step up when shopping for a car alarm. These inputs rely on sudden movements, like a blow or rocking motion, in your car’s chassis. Cheap car alarms have no way of knowing how strong the jolt is, so these give a lot of false alarms. A good system will sense how sudden and strong the motion is and only trigger the alarm in response to movement that feels like an intruder is breaking into your car.

The problem with switches and motion detectors is that many car thieves simply break a window and crawl in through it to hotwire your car and drive off with it. A high-end car alarm will use a microphone to sense the sound that breaking glass makes and trigger the alarm in response. The microphone is programmed to only send an input to the brain in response to sounds of a very specific frequency and ignore all others.