Hi,
This is probably really obvious, and may result in a face palm moment for me, but here goes.
I have an existing float switch to monitor a high water level in a body of water that’s connected to a mains powered warning light (that nobody takes any notice of). If I were to try and add an off the shelf zigbee ‘something’ into that somewhere to give a HA warning when the float switch turns on the warning light, what would I be looking for?
Thanks for reading.
Depends on a lot of things. Approaches I’d look at
a) put a light sensor on it
b) clip a current sensor around the hot wire going to the light
c) wire in a relay in parallel to the light bulb
d) put in a separate water sensor
For my sump pump I did (d), the one I have has two sensor, so I have one that will trigger if the water level gets higher in the sump than it should and another if the water is about to overflow onto the floor.
To monitor the sump pump I did (b) since I did not want to introduce a new failure mode by using a smart switch.
For the septic tank that has a pump the controller is in the basement and i did (a) put a light sensor on the light.
a) It’s an outside blinking red light so I’m not sure this is an option
b) sounds like a goer, but can you tell me what to search for please?
c) this sounds like what I was considering, but couldn’t quite get my head round what I should be looking for.
d) tried one of those which worked perfectly in a glass of water as a test I was convinced this is the way, however, in the septic tank (treatment plant) the sensor gave so many false readings it got torn out. Then I realised the tip of the sensor had been messed about by the condensation.
Given the float is literally switching a live, this is probably what I should be coming off as it’s the most reliable.
Search for a “split core CT sensor” these snap around an existing wire. CT sensors without a split core are smaller but require the hot wire to be disconnected and threaded through then reconnected.
Also, turn off the power open the box up and see how much space you have. The existing controller may have a relay output for an alarm system or may not.
No, there’s just the wiring for a switch, with the float being the switch. There’s no controller. Which is why I was hoping to wire directly off that rather than mess about with sensors and stuff - just couldn’t think what it would be called in the land of Zigbee stuff really.
Interesting setup. The way ours works is there are three float switches. The top one is the emergency float that drives the siren / light. The middle one is the trigger for the pump to turn on. The bottom one is the trigger for the pump to turn off. Sounds like you have no pump and just a switch for the tank getting backed up.
Sorry no, wasn’t clear. There is a pump, but because it’s a treatment plant, the puddle pump lives in the “clean water” chamber and fires out anything in there once the float on the pump itself is triggered.
The float switch I want to wire into for the alarm is literally a float switch hanging that same chamber that lets us know when the pump has failed and the level is too high - by flashing a light everyone ignores 
What would I be looking for in the case of option C as I think this is the easiest solution in my use case.
Zigbee (or wifi) sensor that triggers from a switched live? I keep coming back to considering it should be a relay, but I’ve only used 12/240v relays to turn things on in the past, not to do anything with HA.
Any zigbee relay module with L, N & Switch inputs would do just fine. Something like the Sonoff ZBMINIR2 is commonly available and cheap enough.
Wire it up at the lamp (assuming you have all required 3 cables there) so it’s away from water and job done.
Right on, I’ll give that a search in a bit and see if I can figure it out.
Thanks everyone who’s contributed.
A relay is a better solution. If the light bulb burns out a current sensor won’t see any current.
Still can’t quite get my head around how I’d wire the perm live into it for the float switch to trigger the zigbee element. If anyone could add squiggles onto my “back of an envelope” drawing attached, that’s probably going to help me make sense of it all.
Leave the light wired as is and add jumpers cables to the Sonoff Switch using wire nuts or a wago depending on local electric code.
Line → L
Neutral → N
Line Switch → S1
When the float closes the Sonoff should announce that S1 is closed.
Here you go. Didn’t have an envelope, so I hope MS Paint will do 
Official Sonoff wiring diagram on left, your modified drawing on right
Thanks chaps, appreciated.
Installed and appears to be working perfectly. Now to update my alert to this new sensor.
Thanks all.
Glad you managed!
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Sorry, thought I had - done now.
TBH, I never once considered using a relay to detect power. Makes perfect sense now it’s wired in.
Also gives the added bonus of being able to turn on the strobe warning light to see if anyone notices it - like a fire drill.
