Secondary alarm on the mobile phone

Motivation – creating added value for the fire department

The motivation of this do-it-yourself project was to generate added value for the local fire brigade unit in form of a secondary alarm. There are several reasons for this:

  • Forgot the radio message receiver at home
  • Battery empty, battery running low
  • No signal when alarm occurs
  • Muted, forgot to reactivate alarm sound
  • In the garden, cellar, etc. and alarm not audible
  • Radio message receiver disturbed, defective or in repair

For developers

The entire project is technically documented in GitHub, the Arduino source code is also maintained here.

As this is a German project, the following contents are partially described in German language.

Scope of services, limits, rules and regulations

  • Additional notification sent to mobile phone. Only full alert, no group and/or individual calls
  • Notification by telegram on personal mobile phone
  • E-mail notification
  • No replacement for conventional alerting
  • No transmission of further operational details (data privacy)
  • No guarantee that alarm notification will be sent. Purely secondary, additional alerting

No rapid journeys with the private car on the basis of the mobile alarm system. Equivalent to siren alarming (blind alarm). The mobile alerting is additive, the radio message receiver is the primary alerting device of the armed forces.

Failures, challenges

Integration WhatsApp failed

  • YowSub is a free WhatsApp API for Linux-based operating systems.
  • Implementation is done.
  • SIM card for WhatsApp registration ordered. Registration completed.
  • Only 15 minutes functional. Subsequently, “blocked” error message
  • Support request at WhatsApp opened with the result that now only official WhatsApp software for Android and IOS is supported. Threat: Further attempts would result in a “blocking”.

Purpose Notify-My-Device failed

  • Freely available app for Android and IOS to produce a push notification on mobile devices.
  • Free API. Integration in Node-RED is functional.
  • Standard notification tone corresponds to standard notification tone of the end device. Custom tone always of a doorbell.
  • Two support requests (feature request or workaround) sent to Dutch development team. No feedback received until today


  • Telegram is available free of charge as an app for Android, iPhone/iPad and Windows phones.
  • Native App as web version, for macOS as well as PC/MAC/Linux-based PC systems.
  • Encrypted message transmission, Cloud-based.
  • Free API, development of own BOTs. Granular restrictions of permissions possible (prevent accidental alarms).
  • Functional scope corresponds to that of WhatsApp.

Technical Support Swissphone

  • The power supply of the microcontroller is realized via the Swissphone charging station (LGRA). This required the setting of solder bridges.
  • On delivery, the relay remains open after an alarm is triggered until it is acknowledged on the radio message receiver and is not ready for further alarms until then. By removing the solder bridge BR1 on the circuit board, the relay contact drops out automatically after 10 seconds (open).
  • The Swissphone customer service could not be better and has provided friendly, helpful and competent telephone support on several occasions. Many thanks!

Architecture diagram

Setting up Telegram