The jack headphone connector of the phone is used to make a cheap hard wired alarm. In case of alarm any sound can be played from phone speaker. At the same time a phone call is automatically dial to a chosen contact.
The settings panel is giving the ability to test and tune the state of the alarm sensors. During settings no phone call is dialed. A maximum of four sensors can be wired to the jack connector but availability may vary according to phone model and android version. Optional setting will help to have the functionality when the phone is locked or sleeping.
Each sensor can be set up to signal an alarm either during opening (normally closed) or closing (normally opened) of the contact. A sensor might be setup to act as a latching relay. Latching is meaning that one push is signaling and another push is releasing the signal.
Only one button at a time can be used as normally closed. In that case several sensor contacts can be mounted in parallel.
Normally open sensor will permit to have up to four sensor (** depending on phone model).

**There are hardware limitation due that Google is not maintaining identical functionality for different android version:
1. Below API 21
Media 1 and Media 2 (volume buttons) can only be latching.
2. Above API 28:
Media 0 and Media 4 (Play-pause and voice activated buttons) can only be latching.

Product features:
✅ Automatic alert phone call to a chosen contact
✅ Different sound for each sensor
✅ Works when the phone screen is locked
✅ Option to launch automatically the application when mobile is booting.
✅ Start up is delayed to allow leaving the room.
✅ Alarm is delayed to allow stopping the alarm before dialing or playing sound.
✅ Phone can be made silent.
✅ History of the alarm panel
✅ Alarm can be stopped and start with phone call from chosen contact.
✅ Contact switch can be configured as normally open or normally close.

Wired headphone Dialing Alarm