Now that that's out of the way, I have other gadget ideas
1) update ematch gadget to an igniter gadget with a secondary power source (that will survive more then one use) for multistage, or air start rockets
2) 9 dof imu for interstage coupler to help determine whether a rocket is still pointed "up" to fire the next stage (could be combined with 1)
3) wifi (or Bluetooth) gadget to create local wifi network to arm and verify electronics via smartphone for those that wouldn't use telemetry dongle
4) siren gadget that goes off when motion stops, or it looses network connectivity (aid in retrieving parts)
5) sensor gadgets - temperature, humidity solar radiation, etc... Maybe even a gpio for sensors we can't envision today.
6) servo controller gadget. This would have many, many uses. Could be used as a latch release apparatus like the old spacetech srm to dual deploy out of a single deploy rocket. Or take photo's, enable video, release external boosters, etc... Anything you could dream up using an rc servo inside a rocket.
7) continuity gadget. This could enable the multiple tripwire scenarios others have come up in this thread
You get the idea.