LED switch sensor for appliances

I’ve been considering how to put monitors on appliances… specifically, a stove (for left on alert) and washer/dryer (for finished alert). I’ve seen some solutions for washer/dryers based on vibrations, but that seems to be begging for false alarms. I’ve also seen solutions using power monitoring which isn’t out of the question, but at least with 220v are excessive in cost (and raises safety concerns). Another option is to use a light monitor on a LED indicator, but that not only seems like it wouldn’t be reliable, but would also be unsightly and cover the LED. Assuming I’m willing to void the warranty, would it be possible to connect a simple circuit on/off device like a water sensor to the leads of LED indicators in the device/appliance itself, allowing the sensor to be inside the device, while maintaining reliability?

TL;DNR: In short, could a water sensor be used as a LED on/off monitor? Is this a bright or dim idea (pun intended)?

Tagging @ryan

What price range is not excessive and what safety concerns are you having in mind? You can use the Aeon home energy meter to monitor the energy/power of the stove by installing it at the circuit breaker area without modifying your wiring.

I am using these to monitor both my dryer and stove without any issue.


If my idea actually would work without “side effects” (like the LED no longer working), then to be cost comparative, it’d need to be $15 or less. To be a viable alternative, my max on this project would be $40-50 per appliance. (edit: per sensor)

The Aeon power meter is an intriguing product, in that it’d work for any amount of power and be completely safe (plus have a lot of flexibility for installation), but seems to exceed my price point. Anything on 220v, or with any heavy load, would need to be at least UL certified (eg no beta crowd-funded projects).

If you aren’t afraid of picking up the soldering iron it would be a pretty simple circuit-

You would need a $3 esp-2866 based microcontroller board nodemcu or Wemos would do just fine. Bust the led or wire in parallel, tie the grounds together and wire the positive of LED to one of the GPIO pins on the microcontroller - you may need to throw in a mosfet or a simple transistor in the middle to boost the voltage - use @ogiewon’s ST_Anything and use one of the sensor classes - there are several examples. Post in ST_Anythig thread there is a bunch of interesting things people are doing there.

Remember this is assuming that you have an LED in which case this is on the low voltage part of the circuit pretty well isolated from mains. However make sure it’s an LED not a neon in which case you will fry the circuitry and possible some humans


Here is a discussion on detecting LED state - Arduino and ESP-8266 are equivalent for this purpose - ESP give you WiFi out of the box


Sorry in advance if this is a stupid question, but is this a wifi only solution? I ask because I’d prefer not to have a ton of sensors on the wifi network - I’d need 5 just for the stove (four burners and the oven). Obviously, if this is the only practical way, I’ll clog the wifi (especially given the $3 + solder per sensor project cost), but I’d prefer ZigBee or ZWave.

Nah you won’t clog up WiFi - We have about 50 WiFi devices cell phones, media sticks, dash buttons, computers tablets, etc these things squirt out tiny amounts of data. There are other ways of doing it your can use RF transmitters - but nothing is as simple and cheap as esp-8266. Zwave is very expensive - you may be able to find something cheaper in zigbee but the there is the matter of wiring it up and connecting it to ST

I think you got many replies, but to answer your quoted question,

at least the Centralite/ST/Peq leak sensor, is a bad device selection to monitor dry-contacts or LED voltage, for any condition that will be frequently ON/contacts-closed . I tried it, since I had some spare leaks and nothing else to monitor a fan status contact - When the contacts close, the battery consumption increased a LOT and the battery life went to a matter of weeks/days, instead of months.

You probably would not monitor LED voltage directly anyway, it might need a PCB relay.

1 Like