Hi, I have 3 Ei141 units hard wired in my house. The alarm sounded a short burst in the middle of the night. The unit in my bedroom now has a constant green light and a double red flash every 30 seconds or so. 

Any ideas of what’s up?

As a first step try to clean out the alarm by using a vacuum attachment around the openings of the alarm. If this does not help you will need to replace the unit. If it is less than ten years old you can claim on the warranty. If it is older you can get an Easichange Ei141 replacement head that can be fitted without electrician.

Harry