Noticed this plug on my wall from when I moved into this house, and I just started wondering again about what it’s actually for. This is in the UK, if that helps. It’s on a big bulky box hanging on the wall below my desk next to two regular plug sockets.
Edit: best suggestion I’ve seen here is that it could be a fuse box for an alarm system. Makes sense since this house did have several security systems before I moved in. Also, for added context, this is in a bedroom and the wire coming out of it goes straight into the wall.
Here’s how to find out: use a small flat screwdriver to pull the central white thing out. It’s a cradle for a cylindrical fuse.
If there’s no fuse, it’s for something that’s been removed and they couldn’t be bothered to remove the fuse box and its wiring.
If there’s a fuse, you have disconnected the power by pulling the fuse out of the circuit. Check if something electrical stops working - alarm, shower, cooker, immersion heater, whatever’s on the other side of the wall, loft lights?
Maybe the fuse is there but has already fused, in which case you may want to find or purchase a replacement of the same rating, and find out what electrical thing started working! The fuse rating is written in faint text on the side of the cylinder. If the replace with a higher rated fuse, you allow things to happen in the device that someone thought shouldn’t happen and could blow the fuse to prevent damage or injury. If you replace with a lower rated fuse you risk it going in normal use, i.e. too frequently.