When I first saw this I thought it was sort of cheesy because it looked really cheap. Two pieces of plastic. But I bought one to test it out to see if it was worth anything... it sure is! It's an alarm. Granted not a $300 state of the art set up, but I say it works well... it comes with 2 parts. One goes in your rig where ever you want it...I put mine on the inside door panel so if the door is opened then it'll go off (it detects motion)... the second part goes with you. When the alarm goes off out there it goes off on this unit to alert you. So if someone decides when you are out to open your door looking for your stereo it will go off.... only bad thing is the range is 400'. So say if you go somewhere and are walking around like a mall and get further then that away you won't know when it is going off. But for at home in the driveway, at work or anyplace you can use it it's a cool deal.... just thought I would mention this little item since someone did open my door last night and it went off and worked! I opened my garage door and whoever it was ran away fast as hail... I never would have heard them otherwise since if I am in my room asleep my alarm is very hard to hear and my neighbors ignore it anyhow... but it was $40 bucks and I got it at the Home Depot.... something to consider is all...! I removed my quote so gay, vegetarian, minority, eco-nazis who love Jesus, nuke spotted owls, vote Gore and smoke medical marijuana won't be offend.