Many consumer devices that accept an external microphone will provide "plug-in power." This is a small voltage, usually from 1 to 5 volts at the two pins in the microphone connection.
Apple and (most) Android devices are no exception. Most use a TRRS 4-wire connection with the following output:
TIP = left headphone out RING = right headphone out RING = ground SLEEVE = mic in + plug-in power
The power of the plug-in is usually about 2 V on smartphones and comes as + 2 V on a microphone (sleeve). The phone will only ship it if it detects that the microphone is in place, which it does by checking the resistance through the microphone to ground to make sure it matches the microphone impedance (for example, something like an impedance of 200 to 5000 Ohm, and I hear iphones can be very fussy with this and very close to 1600 ohms).
Edit: this means that the maximum power you can extract from this is very low, about 2.5 mW (milliwatts)
If you want to draw the power of a plug-in module without actually using it for a microphone, you need to make sure that your circuit has the appropriate resistance so that it looks, it has a microphone impedance.
Please note that the power of the plug-in may be similar to the phantom power concept used in professional audio equipment, but it is a different and incompatible standard. "plug-in power" is what makes tiny electret microphones in smartphone headsets work without the need for a small battery.
As for how to actually control a connected device from an application, this is becoming a much more complex electronics. Presumably this is possible if you use the left and / or right headphone output lines to send signals to the device.
thomasrutter
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