Didn't really know how to check to see if this is common knowledge but I find it a useful tool.
If you have an extra little bits power you can put it in front of a second of 2 summed parts with the need of a cable/battery
battery > cable > Power 1(on) > oscillator 1
Power 2 > oscillator 2 >mixer > speaker
the second oscillator will be powered by power 1 even when off. No need for battery and cable either.
osc 1 and 2 are both connected to mixer 1 and 2 if that isn't clear
There are many applications for this!