Fair question! Here’s the list

• Great signal; this is an old barn conversion house so the walls are very very thick and the house is far longer than it is high. It’s always a challenge with the wifi, so I imagine an alarm would be no different.
• Smart and accessible to me, so I can keep an eye on behalf of my father, who often has no phone signal when out and about.
• Modular, so we can buy extra PIRs if needed
• Damn loud - so the neighbours can hear!
• Easy to fit for me/change batteries for my 80 year old father. Ideally a long battery life on sensors too.