Hi my mains smoke alarm is beeping intermittently the unit is old but I’m not sure where to find the model number so I can replace it. Can you help

If you take the smoke alarm down and turn it over the make/model should be printed on the back.

If it is a standalone mains smoke alarm then any stand alone mains smoke alarm will be fine. If however it is an interlinked mains smoke alarm you will need to get another one of the same brand, you can find out by looking at the other smoke alarms.