I have a '69 El Camino and had an alarm for the doors and motion sensor installed - bottom line it put a drain on the battery when sittling for a few days and the battery went dead.
I had a different alarm put in for the doors and motion sensor - same thing happened. I thought perhaps some old wiring had been left in and was causing the problem. I pulled out out all the wiring that was tied in to the alarm and removed it along with the alarm parts. Problem solved.
Now it gets even stranger.
Last week I went to yet another dealer and had a Viper alarm installed for the same doors and motion sensor. Left it sitting for two days. Guess what? The battery was dead.
When I took the ground wire off the battery and put a multimeter across it and the neg. post of the battery - big drain. When I removed the alarm ground and measured from the ground wire and neg terminal - drain gone. So I have now disconnected the alarm and am going to have it removed tomorrow.
Does anyone know what is going on? Does the El Camino have some sort of wiring that the alarm installers don't understand? 3 different alarms, 3 different installers, identical problem occurs. I just don't get it. I need help. Thanks, Bonnie

No, there's nothing strange about the Camino's wiring that is fooling the installers. But: I would not install a motion sensor or glass break detector on the car. They simply cause too many false alarms. If you want to keep the car, put in either a hidden kill switch or a fuel shutoff.
Here's how you steal a car with a motion sensor. You shake the car and hide. The owner comes out and re-sets it. You shake it again in an hour. He resets it. You shake it in two hours and he shuts the alarm off. Game over, car gone.
In all seriousness, everybody is so used to alarms that you usually assume it is the owner who tripped the alarm. Unless the alarm horn and wiring is very well hidden, all it takes is one yank on the wires and the horn goes silent. An alarm keeps the honest people out of the car, but only costs the pro about 5 seconds to kill it. They all work on the same theory with door switches, an ignition relay and a horn. Ask the installer how long it would take him to get around the alarm system. You won't like the answer.