I’ve got a Yale premium wireless one, and it is definately insurance approved by M&S as long as it serviced every 6 months (bloke changes the batteries, charges you £40 and gives you a certificate)
Works well, and is easy to install. You can have multiple sirens, PIR, pet friendly PIR’s door jam alarms (good for the shed/garage) and it calls a preset list of numbers when it goes off.
I am about to mod a siren, to include a sound bomb inside to finish mine off.
NB: Mine definately works, as my Dad set it off when popping into the house to go for a pee, whilst I was on holiday skiing. He was quite surprised when I called him and asked him if he was in the house and could he reset the alarm 🙂