Something in my kitchen (or possible living room) is making a very soft beep every minute.

I’d heard it a bit over the last few days, but I assumed it was water dripping in the extract fan outlet. It’s (gasp) actually sunny this morning, which made me pay attention and notice the regularity of it.

It’s not the CO detector or the smoke detector (which I learn in passing appears not to actually be wired to the mains). The only new electrical things in the kitchen in the last year are the new hob (very different kind of beep) and the water meter (no, me neither, but I have stuck my ear up to it and it’s not that).

I suppose the next step is to turn the mains power off, but I need the doorbell for an expected tradesman, so any ideas in the mean time for something that would suddenly start beeping like that?