UK Government states that all businesses must have a fire detection and warning system of some shape or form. However, the types and number of detectors you require will be dependent on the type of building you occupy and the work carried out in it. This will be made clear in your Fire Risk Assessment.
But, your responsibilities as a business owner go much further than simply purchasing an alarm. All Fire Alarms must be installed, tested and maintained to a high standard. Staff members will also need to be trained on how these systems operate, with fire drills needed to be actioned and recorded regularly.
To comply with BS5839-Part 1, a fire safety code of practice, alarm systems must be maintained by a professional every six months without fail. This is also something most Insurers will require when creating policies for properties used for business purposes.