Who knows the simplest hardware mp3 player?

Question

Mobile devices

So that when power is supplied to the player / board, music immediately starts playing.
I'm trying to implement the automatic inclusion of music when entering the room. ( for example, like here ).
I think that if I manage to find one, then by applying voltage through the motion sensor, I would be able to complete the task.
Soft solutions, raspberries, bluetooth seems to me fat for the house: either a long inclusion, or a constant inclusion, which leads to energy consumption.

Answer 1

Here