Pool alarm suggestions

[Kerry Baird]

With new technology coming out regularly, I am putting the old question through new paces. I want to see if anyone has used pool alarms or door alarms that work well for guests in your STR. Amazon has some packs of alarms, some with a remote, some with an on/off switch. They generally are two peel and stick components; when the two pieces are near each other there is no sound, but someone opens a door and a loud alarm is emitted.

I have been running a few years and no one has asked for them until now.  A grandpa has booked and has small grandchildren and he'd like alarms.  I can do that.  Which ones?