Anyone know of a sensor that can detect a reflection

I have a Frient sensor on my old electricity meter which detects an emitted light pulse to record energy use. 6 months in and it’s been perfect so far.

My gas meter is also old and I thought there was no way of reading it, but I noticed that the #6 on the dial as it rotates has a wee mirror on it. Each rotation records 0.01m3 of gas consumed.

So, as per the subject: Does anyone know of a battery (pref Zigbee) sensor that can detect a reflective surface so it can be reported to Home Assistant?

In case it’s relevant, the meter is a Sensus U6 Diaphragm Gas Meter

I’ve just seen one way to do it using an ESP8266 but it’s waaaay too advanced for me.
(and I live in an apartment where the meter is too far for wifi)

Maybe useful for someone as a reference

You could show us a photo of your meter. Chances are good, that there’s also a magnet, if there is the reflective bit.
If you only have the reflective bit: I doubt there’s a readily usable sensor for that. In that case, I’d try to hack the output of a reflective light barrier sensor to a zigbee window sensor. From there on, there are known solutions.
If there’s a magnet: Skip the hacking bit and just use a window sensor. Like this: Gas meter from Xiaomi/Aqara door sensor (ZigBee)

Pictures below.
I’m pretty sure it does have the magnet as I think it’s a common feature on the mechanical roller counter meters, but there’s a plastic shroud covering the dials and it looks different underneath to others I’ve seen which are recessed to get closer to the magnet.

To my eyes it looks like it’s a larger display panel with a built in sensor reader with cables coming from it. I think the cable may have had an RJ11 on it at some point, but all of the meters in the cupboard have had them removed and are cut loose ends.

The cable that comes out of it could be one of these? (clicky link)

To me it would make most sense to try to figure out how to use the existing sensor. (The cable strongly suggests, that there’s one.)
With a multimeter you can simply check which 2 wires belong together. Between 2 wires should be 0 ohm resitance, unless the magnet passes the sensor. The other wire pair should then be other way around.
If you have figured that out, you just need to connect one pair (which one doesn’t really matter) in parallel to the reed sensor of a window sensor and you are ready to go.

I gotta admit, I’d be slightly nervous about hooking up a multimeter to the cables.

Primarily as I think one of them may trigger a tampering alarm.