DIY Audio Recorder and Player kit,

Record standalone or Download Music via USB:

MP3 files can be created using Audacity:

These can be downloaded on the recorder module, which appears to the computer like a disk drive:

Below: 

In normal operation, the MP3 is played when the button is pushed.

 Instead,  a 3V relay contacts are used to simulate a pushbutton.

In this example, when the  ultrasonic sensor is triggered, Pin 16 is momentarily brought, simulating a pushbutton, triggering the audio player, then reset. 

The second 'while' loop is to prevent continuous retriggering of the audio.

Note: This example uses Bluetooth radio, but the HC-12 could be used instead if greater range is needed.

Below: When receiver receives the word 'alarm', happy face shows for a few seconds.