Couple ideas, depending on what you have:

• When the warm water pipe heats up
• when the water heater starts drawing more power
• when the water meter detects warm water usage in the evening
• when the sound volume goes up in the bathroom
• when the weight sensors go off under the shower (or around it as you get in)
• when a movement sensor detects movement in the shower
• when a magnetic door sensor sees the shower curtains open
• when you press a (waterproof) button in the shower
• when a weight sensor under the shampoo holder detects less weight

mmwave sensor, humidity sensor, and/or monitoring your water heater power usage. any of those 2 should work.

I am actively working on a bunch of ML algorithms for home assistant for exactly this type of thing, detecting ‘activity’ per room.

Are u nekkid, but warm, and wet? You’re in the shower.

Flowmeter on the shower head or down in the supply lines to the tub/shower?

Any reason a flow sensor wouldn’t work?

sounds like you could use a clapper

You could use a classic dead man switch: Place several buttons around the whole place - basically everywhere except in the shower. Once you stop pressing any of these buttons for - let’s say - 30 seconds you can assume you’re taking a shower.

How about a simple on off toggle inside your shower handle? Stupid simple and works anytime the waters turned on.

Motion sensor positioned really close to the shower controls so it doesn’t see anything but them/your hand moving.

The bigger question might be how do you turn it off? I like the vibration sensor on the shower head

Not sure if you have access to the pipes leading to the shower, but the droplet does what you’re looking to do.

https://hydrificwater.com/

I use a humidity sensor, motion sensor and a helper that shows the change over a period of time. If the humidity raises fast (+2%/5m) and goes over a certain amount (unique, depending on your room’s climate) the bathroom automation changes tracks to hold the light at 100%, turn the extractor fan on, and well, how you stop the automation depends on you. I let it stay on for 15 minutes before waiting for motion. Small tips: For me the humidity triggers the automation within 15s-1m of showering, which is okay for me. Motion sensors typically use IR to see movement. If the room is too steamy it might struggle to see you. Also, it cannot penetrate glass. It must have a line of sight to you.

The best alt I think would be mmwave presence sensors, but they’re pricy and require a wired connection.

Vibration sensor that detects when water starts flowing through the shower head

Crossposted from showerthoughts

I would go for a simple humidity sensor. You just need to do a bit of data collection first to get a baseline of “what taking a shower usually looks like” and then based on that create the automation.

The only problem with that is that depending on how accurate you want it to be, you may have to wait a while to take a few measurements until it triggers the automation.

For something like mood lights I would just use a ZigBee switch if I’m being honest though.

Multiple waterproof 4k cameras pointed at the inside of your shower from every angle and image recognition by some AI that detects when a naked person enters.

Don’t forget to use Wifi and no firewall