DIY fire alarms.

Because you haven't read the Scottish legal requirements for fire/heat/CO alarms in houses.

all houses

To be enforced by making them unsellable/rentable if you haven't don't it.

So pretty useless if it's your "forever" home

But after being made compulsory how long afterwards will most of them cease to work due to dead batteries, not being replaced at end of life, chocked full of dust or simply removed because of too many false alarms. Will we all be required to pay for an annual check to certify that the detectors are still in place and working.

Why would you need a CO2 detector if ALL of your heating and cooking needs are going to come from wind and solar?

Why 7W per device? A battery powered smoke or CO2 detector alarm can run for over a year on a single PP3 battery. BUT Possibly only a few hours if the alarm was continually sounding. Is the specification for you mains powered units a maximum of 7W (when in alarm mode) and much much less in standby detect mode.

which is why it's stupid

Checks will simply be done as part of new occupancies, either tenants or owner

Makes sense in the letting sector where churn can be high, but not for OOs where it can be much lower

these are not CO2 detectors, if they were they'd be buzzing all day long. They are Carbon MONOXIDE detectors.

You might, if there was a power cut, be stupid enough to bring a petrol generator indoors.