If you are using a leak detector/water sensor, do you have a recommendation?

I use something like THESE.

I use the one that works with Simplisafe security system. I put it next to the water heater and it went off in the middle of the night once because the water heater failed and was leaking everywhere. It saved a basement flood, so well worth the security system just for that

I use the Gizmode Water Screamer. It is LOUD. If it goes off, you won’t miss it.