I've had D-link water sensors for several years, and have been happy with them. The most recent generation uses a primary sensor which plugs into 120V, and battery-powered satellite sensors for additional locations. All report through their app, which doesn't have a monthly fee, and also have audible alarms to alert you locally.
The only downside for me has been that I don't really have a suitable location for the primary sensor that would have an available 120V plug, and place it somewhat centrally in the house so it can service the satellite sensors while serving a leak detection purpose. For that reason, I've got the primary plugged into a wall outlet in our pantry with the water sensor cable still coiled up. It's a bit of a waste of sensing potential, but it works.