As of today, all homes in Scotland must have an interlinked smoke alarm system throughout the house whereby if one alarm sounds they all must sound.
For my two-bedroom, two-storey house, I am legally obliged to have a heat alarm in the kitchen, a smoke alarm in the lounge/living room, a smoke alarm at the bottom of the stairs and another at the top of the stairs outside the bedroom.
I don't know what the penalty for ignoring the law is. I have been unable to find that out. However, your insurance coverage may be void if you have a claim and were found not to have a compliant system fitted.
Owners of houses less than 10 years old should already have such a system installed as they have been included in new builds for the past decade.