Obviously, the one component everyone probably knows a lot about, is the ability to trigger the alarm system manually via the key fob. But let's go ahead and assume you're not constantly staking out your own vehicle, how does the anti-theft system do its job? Most often, a car employs a number of sensors that detect movement, pressure, and much more. If your car starts moving when it shouldn't be, if the air pressure inside a vehicle changes - perhaps due to a broken window if the door is being meddled with by something other than a key, et cetera... the alarm system will trigger, and your would-be thief will hopefully be frightened away.
Some alarm systems are even more high-tech than that. They'll employ actual perimeter sensors, which work almost like cameras, scanning the surroundings and making sure to trigger if anything changes or keep track of the surroundings if the vehicle is towed away. If you have any questions about Toyota anti-theft alarm systems in particular, be sure to reach out.