We built a setup like Larry's above for the layout at the InfoAge Science museum. When volunteer guides from the museum bring visitors to the layout a motion sensor is activated. This is a typical sensor used for many things for house current.
This turns on the layout room lights and layout power.
We have big red buttons on the layout sides, like an emergency off button look, that activate a timer to start a train. We have it set for about 2 laps around. The timer is one that is found on eBay that operates on 12 volts. The relay on the very small board can handle up to 10 amps of AC current.
In the attached video, you can see two of the big red buttons, one the low left and one on the low right.
The layout is 10 x 19 with 4 levels and 3 levels of train track separated into 3 individual loops.
