Using shelly1 SW input for downstream devices

Hello, I recently bought and hooked up a shelly1 to my water heater, which is controlled by my home assistant installation. I want to know when the water heater is actually on (it might be powered by the switch, but it turns on only when the heater thermostat does). Since shelly1 doesn't offer power monitoring, I was thinking I could use the SW input (which is normally used by connecting it to a wall switch) and connect it to the live wire after the thermostat. Then setting the device to "detached mode" I'd get the sensor input in home assistant but the switch won't automatically act based on that input.

Sadly, I couldn't find any diagrams or understand how the internal connection of shelly1 work. I have no idea if connecting the live wire after the thermostat back to the SW input on the shelly is going to cause any shorts or if (as I expect/hope) the device uses the SW input just to measure the voltage and doesn't actually connect to anything else. Any clues?

Thanks

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