"This is an economical detector head that complies with building regulations. Comprehensive fitting instructions made it easy to install. The 10 minute timer is a useful feature as I was installing one in the kitchen and the previous property owners had removed this detector head to prevent false alarms - crazy I know!!"
"The key thing about this product is that it has an internal battery. This means that when it is first plugs in its charges itself up and will cover several hours if the mains is disconnected. After mains disconnection it shows a red light when the battery is dwindling and again whilst it recharges afterwards.
Hence, getting a mains alarm with a 9 V battery backup is a waste of time and money, unless you really expect to the mains to be down for a prolonged period of time, such as days.
The only downside is that the connector supplied is, as with the other alarms in the range awkward in that it protrudes at least an inch to the back of the alarm and you need to buy a sub base in most instances For installation."