Safer Alarm – 7400 competition entry

The Dangerous Prototypes Open 7400 competition winners have been announced, congratulations to all the well deserving winners.

The Safer Alarm did not get a prize, but the project is still a great idea :), so please have a look and think about providing at least some ideas!

This competition has helped to generate some interest in this site (and traffic) with visitors from ten countries in the first two weeks, thanks to Dangerous Prototypes.

Safer Alarm – 7400 competition entry

The mark 2 version of this circuit which was entered into the Dangerous Prototypes 7400 competition has now reached successfully five weeks running on it’s own backup super capacitor. During this period it has maintained the alarm status and powered the indicator LEDs on more then 25 occasions.

The first version ran for seven weeks, but with less LED activity.  So there is room to balance costs and backup time with the current 7400 design. An order for some pico power PICs will be sent soon, so the mark 3 version with a few more bells and whistles can be prototyped.

As always, if you would like to be a part of this project in any way, leave a comment here, or at the project site at Launchpad.

Safer Alarm – 7400 competition entry

There are several situations where common alarm systems fail to provide any indication that something bad has happened, such as the limited time sirens can sound. This varies according to your local/country regulations, and but when you return, the siren will most likely be off.

Alarm strobes, if fitted are highly visible deterrents, but:

  • generally provide no external fail safe indication
  • no indication if power totally fails
  • relatively heavy power use, so require a significant battery

Alarm strobe lights can run from battery and be left on for long time, but if the the power has been cut off, will your alarm survive without power during your annual holidays?

This system provides a simple, effective and practical enhancement to existing alarm systems to tell you if your alarm has been triggered, tampered with, or lost power. It has been designed to minimise risks by:

  • giving a safe to enter signal (Green led ONLY)
  • has fail sale indication (NO indicator = issue)
  • indicates if alarm system has been tripped (Red led)
  • indicates if the alarm system has totally lost power (Yellow LED)
  • can survive on it’s own power for 2+ months

The schematic is shown below, and the Eagle version is here.

Safer Alarm -  schematic
Safer Alarm - schematic

Informal testing has shown this circuit works well. It also survived 7+ weeks without power and around fifteen to twenty tests of the indicators.

Safer alarm
Safer alarm

Further testing using an Arduino and LiveGraph software shows a ‘pretty’ graph of the charging of the super capacitor. I also wrote lots of test code to capture the discharge cycle and occasionally turn on the LEDs, but this went badly wrong as the Arduino test circuit injected power into the system via the flip flop inputs when it was logging, or drained power from the system when left connected, but switched off.


safer alarm test setup
safer alarm test setupCharging the supercap (LiveGraph)


Charging the supercap (LiveGraph)
Charging the supercap (LiveGraph)



I have just started an open source project to get community help to take this project further. If this project was awarded any prizes,they would be used to encourage further community input to this project (and not given to me or my family, friends, relatives).

Further enhancements could include the use of a pico power AtTiny PIC, this would also open opportunities for more enhancements, including more indicators or count of times alarm triggered, and remote indication, whilst keeping low price and matching input signals to typical alarm active collector active low outputs.