I'll have to look at the power bus a bit more. Would be interesting to see if I can determine the difference from other power spikes. There's a company near me that does whole house power device detection. Place a current and voltage sensor on the main line for the house and look at the power signature as devices are turned on and off. Can detect when the refridgerator starts running, or furnace, microwave, washer, dryer, various types of lights, etc, etc. Very interesting technology. Would imagine the same can be done to some degree with just the voltage at the 12V outlet, and used in combination with other cheap techniques it might be enough. -Adam On Sat, May 31, 2008 at 10:14 PM, David VanHorn wrote: > When the interior light turns on, there's an easily detectable glitch > in the 12V bus. > This has been used for car alarms since the 70's. > You can see it anywhere on the bus. > > You can't easily tell it from other spikes, but then again, does it > really matter? > Engine on and off can be seen from the alternator whine and the > voltage of the 12V bus. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- EARTH DAY 2008 Tuesday April 22 Save Money * Save Oil * Save Lives * Save the Planet http://www.driveslowly.org -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist