Hey All,
Back some 7 years ago when I had no kids and more disposable income I purchased 7 nest protects, fast forward to now, I get the dreaded I need to replace them all alert. Now I’m not to happy with the nest eco system anymore, their approach to api post google acquisition and their price among the main contributing factors. I set out on a replacement, my criteria being the following;
- Has to be cheaper
- Local and non cloud preferred
So my journey started with a purchase of 6 x-sense interconnected fire alarms for about £80 (the cost of one nest protect FYI).
My next step was to make them smarter, my go-to device is esp32 using esphome. I set about using the gpio functionality to sense a voltage increase which the esp32 could post back to HA and trigger an alert. I’m not electronics expert but my first thought was to couple on to the siren power! For what ever reason (still unknown) I couldn’t get it to work. I then decided to use my multi meter and painstakingly test every connection on the fire alarm board whilst triggering the alarm. After checking everything I found no more than 1v during an alarm trigger which isn’t enough trigger the gpio voltage sensor on the esp32.
After lots of fiddling and some kind help from this forum I used an optocoupler to turn a low voltage contact into a relay on the 3v to the gpio on esp32 as per below.
The above photo shows my choice of detecting the mere 1v pulses when the alarm goes off. Black goes to the battery, red goes to a position the spits 1v pulses when the alarm goes off. This then goes to an optocoupler below;
The blue and green then go to the gpio pin and the 3v respectively.
After a dabble with my new 3D printer and a dodgy looking hole punched into the alarm for the wires to come out, it looks like this;
Wel to my amazement I had a working solution!
Couple of points before I close out,
- It doesn’t do carbon monoxide, I have standard alarms for that, maybe I will make them smart one day.
- The alarm I have butchered is not one I’m using to detect smoke, it’s specifically chosen to listen for the interconnect comms from the others and then interface into ha. So not creating a safety problem.
- Unlike nest it’s not able to tell you the location, however if there is a fire the location is largely irrelevant to start with!
Hope some people find this useful, my explanation of some of the electronics involved is likely to be wrong as I’m a total beginner!
Sam