I think he mentioned Aico smoke detectors. Hallway, Landing, Kitchen, Living Room. I need to think about the home alarm as well - totally forgot its best to do it all at once!
Aico are good units - but hardwire them. IMO radio is for when you
can't hardwire, hardwired is better - except for the inexplicable fact that Aico decided to make some features only work over radio. Bear in mind that the radio modules for Aico kit cost about the same as the detector heads - so going radio puts the cost up considerably.
On their website, they have a lot of advice to help you chose the number and type of detectors to fit. Of course, as house differ in arrangement, each will have different requirements. The basic minimum is a smoke detector on each floor - typically hallway and upstairs landing. You may want a heat (& CO if there's gas appliances) detector in the kitchen, you may want a heat detector in the garage.
While it's not mandatory for your own house, in a rented house it a legal requirement for a CO alarm in any habitable room with a solid fuel burning appliance.
Last year I renewed/upgraded the detector in a one bedroom flat - probably overkill but smoke in the vestibule, heat&CO in the kitchen, and heat in the garage underneath, and a test/locate/silence switch. What was most annoying is that I'd managed to get a cable from the existing smoke location to the kitchen when the ceiling was brought down by a water leak upstairs, and I could cable from the CU to the garage, but I had to add two radio modules to link them which added (from memory) something like 50% to the cost of the units.
I'm thinking of swapping the heat detector for a heat&CO as there's a gas boiler in the garage - I have somewhere else I can use the heat detector. I initially didn't fit CO due to the risk of false alarms from car exhaust fumes - still not sure about that, but the guys that do the gas safety checks always check if there's a CO alarm (there's a free-standing battery one so they can tick the box).
... my kitchen fitter said I need to make sure the electrican had as a registration.
As I mentioned above, it's one of the options you have available to you. TBH, it will almost certainly be cheaper to use a scheme member than to go down the self notification route.
many intruder alarms are wireless now and can generally be fitted in less than a day.
As above, if there's the chance to hardwire then hardwire. Wireless options all have drawbacks, and in principle are all susceptible to jamming - possibly with no warning for long enough for someone to get in and get out.
