I received the garage door detector from SmartHome yesterday, and it work like a charm. This device (mounted on the inside of the garage door) actually detects the angle of the garage door to determine if it's open or not -- vertical will send a "closed" signal, horizontal will send an "open" signal.

I mount it close to the top of the garage door. That way, even if it's opened 1/4 of the way, the top horizontal panel of the garage door will not be vertical and will send an "open" signal.

I'm sure it doesn't use mercury, because there were no "DANGER - POISON" warnings. Although a mercury switch would be a great idea to sense angle. I have an extra one from an old analog thermostat I replaced.

Roland