Automatic leak detection systems for rental properties

[Gusatvus Johnson]

I'm thinking of installing a leak-detection system in my multi-family rentals. I've seen several in the $200-$500 range that get installed where the main water supply comes into the house, then monitor water flow and send you an alert (via text, email or whatever) if they think there may be a leak.

My main goals are to detect pipes that burst during freezing, as well as to detect running toilets or other small leaks that my tenants don't bother reporting before they cost me hundreds of dollars in water bills.

I'm wondering if anyone has used one of these systems and how well they've worked. Did it detect leaks properly? Were there a lot of false positives? Are there any systems that can detect leaks at specific fixtures, rather than just telling you that there is a leak somewhere in the house?