I have a Beckhoff PLC that controls the “critical” parts of my home automation (main lights, blinds, underfloor heating) and then I use HA for additional functionality on top of what the PLC does. The PLC is connected to HA via the ADS integration.
For controlling the heating, we have EnOcean temperature sensors (Thermokon SR06 LCD 2T Temp) in each room, which have solar panels and also built-in batteries.
These do however run out of battery every once in a while (not enough light at their mounting position), which leads to cold rooms by the time we usually notice it (we don’t really see it in advance as they don’t report low battery to the PLC). The sensors update their value whenever the temperature changes by some threshold, and that apparently doesn’t happen as often at night as it does during the day.
So I tried to reset a 12-hour timer everytime the sensor sends a value and trigger an alert on its expiration, but that somehow gives false triggers due to the way the sensors work because it’s perfectly normal for them to not update at all when it’s dark, but then update every 15min when the temperature changes quickly during the day.
So how could I detect when one of these sensors’ battery goes flat as quickly as possible (so without using a very long timeout) so that I get an alert before the room gets cold?
One option could be to add a second temperature sensor in each room, and compare the values of both sensors. When there is an abnormal difference you can conclude that one of the sensors isn’t working correctly anymore, hence the battery could be flat.
This extra sensor does not have to be the same as the current ones: it can be any (cheap) sensor, as long as it can be monitored from HA.
But that would be additional hardware that costs money, has to be maintained (batteries, …) and is also unnecessary since we already have the sensors I’m writing about. We also have quite a large number (2 buildings on the same property, 18 sensors in total) of these temperature sensors so I would need just as much of these secondary sensors…
I would basically just need a way to ignore missing updates during nighttime but reliably trigger alerts when they don’t update for a significant time during the day…
True, but these don´t have to be as expensive as those EnOcean sensors. Any cheap sensor would be good. Redundancy is a common solution for “critical” systems.
But if somebody comes up with another solution it would be great.