This is the case for a small IOT capable MP3 Player I use as WIFI doorbell.

The idea is to have one device that listens for the doorbell that sends an UDP broadcast message if a sound is detected and this little guy that plays an MP3 if it receives the message.

Of course you can use if for other purposes as well ;)

FreeCAD source file included!

Some basic sample code will be available on my blog soon -> http://blog.digidigtal.de

BOM: 1 x D1 mini ESP8266 (e.g. from Aliexpress) 1 x DFPLAYER MP3 module (e.g. from Aliexpress) 1 x 20mm x40mm 8 Ohm 2W Speaker (e.g. from Aliexpress)
4 x M3 x 10mm screws/bolts (e.g. from Aliexpress)