How often should I test my smoke alarms?

The 18th Edition wiring regulations suggests that smoke alarms and heat alarms should be tested monthly. 

Did you know that most smoke and Heat alarms have a expiry date of 10 years and should therefore be replaced. A label of the expiry date is displayed on either the outer shell of the unit or on the smoke alarm head when removed from the base. Most Smoke alarms use a 9v battery, use batteries generally have a 5 year expiry date. When a battery needs replacing, the smoke alarm will randomly bleep, highlighting that there is an issue and needs replacing.