Whether you're obliged to fit smoke alarms or not depends on the status of the property you're letting. If your property is a registered HMO (home in multiple occupation), you are required to take all manner of fire safety precautions - including fitting smoke alarms and marking emergency exit routes. You're best advised to consult your local authority on what exactly they require for HMO properties.
But if you’re renting out a family home or a one or two bed place, you won’t be governed by this legislation and astonishingly you aren’t legally obliged to kit your rental property out with smoke alarms. This is one area where we’d advise all landlords to go beyond their minimum obligations. Imagine the hassle, loss and potential tragedy that you’ll have to deal with if you place did suffer a serious blaze. It makes sense to have them installed. It’s relatively cheap.
But it is one thing to install smoke alarms and quite another to ensure they’re working. Make sure you remember to include them in your maintenance programme. Show your tenants how to test them, and change the batteries between tenancies. It's a very small price to pay to protect both your property and your tenants.