Had my gas safety check two hours ago, He fit a new carbon monoxide alarm. It was fine when he was here then he left and it's been doing two very loud beeps every 30 seconds ever since. Googling tells me the batteries might be dying but the model he fit is solid and I can't open it up to put batteries in, there's no cover or screws on the back of it (see pics) it was brand new in the box when he fit it.
Anyone have any ideas please? It's driving me mad.