Networked Smoke Alarm

The objective of this project are:

  • To add a networked smoke alarm within our home automation 19" rack cabinet.
  • To see how well our chosen device works, to see if it could be used throughout our next home.
  • To see how much power it would take from our 12V DC [PR] UPS.

As part of this project we also intend to test out the inter-connect capability of these smoke alarms to see if we only need one connection to our Home Control System (HCS) or need to connect each smoke alarm individually. Ideally, each would switch individually so that we can know which one went off, whilst also having all alarms sound if one goes off.


For maximum protection is it better to use a combination of both ionisation and photoelectric smoke alarms. These different sensor types operate on a different principles and therefore may respond differently to various conditions. Ionization sensors may respond slightly faster to flaming fires, whereas photoelectric sensors may respond slightly faster to smouldering fires.

Aico Ei Professional 12v Ionisation Smoke Detector (EI100R)
This project is based around the Aico EI Professional 12V Ionisation Smoke Detector (EI100R). The datasheet (PDF) is available online and shows that this device is happy with a supply voltage of 10.2 to 14 Volts DC. This allows for any voltage drops on long cable runs but, the device uses so little current (standby current = 150 microamps (max), alarm current = 60 mA max, 30 mA min), this is not likely to be a problem.

We plan to connect it with standard 6-core alarm cable as this is cheap we always use wired connections where possible, as they are the most reliable.

This smoke alarm carries the BSI Kitemark to indicate type testing to BS EN14604:2005. It will meet the requirements of Grade D (and exceed the requirements of Grades E and F) as defined in BS 5839: Pt.6: 2004. It carries the CE mark to indicate conformance to Electrical Safety and Electromagnetic Compatibility Directives. Basically there are no legal issue in installing one in your home.

The unit has a built in sounder giving a minimum sound output of 85dB(A) at 3m. Frequency range 2200/2800Hz.

View inside the Aico Ei Professional 12v Ionisation Smoke Detector (EI100R)
Inside the alarm.

View inside the Aico Ei Professional 12v Ionisation Smoke Detector (EI100R)
Another reason why we chose this device is that it has both NO and NC relay contacts, rated to 24 Volts/1 Amp resistive. It also supports alarm interconnect, meaning that if one alarm goes off, they all do. This is achieved with a single wire and we will connect them all back at a central point.

We are well aware that there are wireless Z-Wave smoke detectors but, our preference is to always use wired technologies where possible.


These devices are connected to our USB I/O board. On sounding our Home Control System (HCS) activates the main alarm sounders with our home and also sends notifications (SMS and email) to our mobile phones.


This project is working exactly as we planned but, we have an issue with these alarms. Whilst the are functionaly very good, they are not very subtle and are far from being stylish. We are now using a different smoke sensor.

Further Reading

FireText Smoke Alarm
The FireText Smoke Alarm is a much more complex and expensive example of this project. This battery powered device accepts a SIM card and can send text messages to you on activation.

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