I arrived at Ms M's; she directed me to the alarm which was clearly audible. I used the ladder that she had provided and after watching a couple of youtube demonstration of how to get the lid off the alarm; neither of which were useful!! I managed to get the lid off; we discovered that the alarm was wired and had a battery as a back up. Ms M told me she had counted the seconds between the beeps; she told me that it beeps at 37 and 53 second intervals; it had been keeping her awake that long!! Ms M was happy not to have the battery replaced at this stage as she wanted to be able to sleep! She will be sourcing an electrician as she believed the alarm was faulty. She hoped that her other two smoke alarms did not start keeping her up. After a lovely chat where Ms M said she had lived in her home for 46yrs; I left her to enjoy the rest of the day.