The most valuable thing of all is good trustworthy neighbours. But to reinforce that I also have:
Hive for the heating, I just set mine to come on at 10C and forget it. When the weather gets better it just never comes on so you don't use any more gas than necessary. But if you are going to visit, you can just dial up the temperature from your phone and turn on the hot water.
Hive also has door/window sensors, I have one on the front door so I can see when the neighbours drop in even if the alarm is off.
And (but a bit more expensive) Hive has lights that you can programme to come on/go off to make the house look lived it. But simple timers can do just as well.
Amazon Blink XT2 webcam in the hall and one in the garden (just discovered we have visiting foxes). The newer 3rd generation Amazon Indoor?Outdoor is a subscription service but the old ones are free cloud service, can be picked up on eBay. But I didn't go for a Ring doorbell.
Alarm system - also connects to the internet. My neighbours have the keys but not the alarm code, so they WhatsApp me, I disable the alarm, they check the house, I see them leave using the Hive door sensor and/or Blink XT, alarm goes back on. If the alarm were to be triggered, the sensors take photographs.
But with everything so "connected" you also need a permanent internet connection and I haven't found a cheap way to do that as you always have to have the phone line too.