They have been very useful because our children drive our vehicles. They are aware that leaving them plugged in is part of the agreement, and it is for their safety. And it is a choice...we don't feel we have to spy on them constantly, but knowing we can choose to see where they are, and if they are speeding alleviates some of the concern. We also feel better knowing that if the car broke down, we could find them easily. And of course, in case of theft, we could locate our vehicles. For the cost, the devices bring cheap peace of mind.