Well, if it's a small enough door...

One more thing here. The voltwatch is not a loaded device. It relies on the existing load.. RX, servos as the load. So, it cannot be used unless the system is energized.. that is, that the receiver is powered on and supplying power to the servos. Other than that, it is not something that you can just plug into a battery and expect to get a correct reading. It will be high, and not loaded.

For an out-of-circuit test, an ESV must be used, or at least a voltmeter that takes a reading across a load of some sort.