Trying to get ideas on how to make a backup ejection system in case the motor-based ejection charge doesn't work or fails to adequately pressurize the airframe.

Found an idea on the web that used a modified Radio Shack pager, but it seems the time delay could be too long. Could use an altimeter, but I deally it would the charge would not go off unless there was a problem.

Considering the possibility of a timer of some sort, where the timer is deactivated by the chute being deployed, pulling a pin and breaking the connection. What would be the best way to start the timer?

Fred, there are several timers that a G activated on the market. You could also build one, and integrate a G switch.

I would not worry about the charge going off after the parachute has ejected. let it go, and do not worry about it going off...no big deal. Set the timer for a couple of seconds after the delay is supposed to go would be my thinking.