Sensor to indicate if the humidifier is empty

Is there some cheap way to check if my (DIY) humidifier is empty and needs to be refilled with water?
I only need to know if it is empty or not.
Can a water leak sensor be used for this, just “in reverse” ?

I’d make something with a couple of metal rods reaching to the desired minimum depth in the water container, and an ESPHome device checking the resistance between them reporting back to HA. I’d imagine most leak sensors aren’t intended for “normal submersion” as they’d be designed to shout only if wet.

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If you do go the ESPHome route there are some ideas here you could use:

You would have to invert the output but that’s not an issue.

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Interesting. I will look into the resistance option.

How about using one of those power (or energy) measuring plugs, probably with Tasmota ? You would look for the plug being on but drawing little power for “fixed time”. Bit of tweaking needed to get the timing right.

I do similar for determining whether the wash cycle of my dumb washing machine has completed.

Many leak-sensors work fine “in reverse” and can be used.
I personally use one of these

to detect if the tank I use for watering the plants on the terrace is empty.

If you need more control over the actual water level (maybe not for a humidifier) I have one of these guys ready to be installed, but have not tested it yet…

I went with the Aqara water sensor. Simplest solution. It’s been in the water for almost a week now.