I had a roofer come by in December to fix a leak and it appears the leak is back.

What they do: 1. find moisture / leak / fix2. air circulation  fans/ open windows day and night3. remove drywall, any fabric, porous material and replace  any new material you bring in will have some mold Everything has mold, it's in the air.

While the primary purpose of these vists is routine maintenance (clean/change HVAC filters, check backup batteries in smoke/CO alarms, etc.) it provides an opportunity to survey the state of the property and find small issues (the leak under the kitchen sink) before they become large problems (the students will not notice, or remember to tell you, about the leak under the kitchen sink until water drips from the ceiling below)- hold tenants accountable for utilities.  

The sum total of my work with the tenants has been this:Advertise the property, show the property, accept applications (and fees), screen the applicants, sign the lease (5 hours or so upfront).The tenants called once about a leak in the drain under the sink.

The major one was replacing a roof on a barn that was disclosed on the property condition disclosure to leak.

The leak had gone undetected because my renter failed to transfer the water bill to their name – and therefore had not been aware of or even paying the water bill once since moving in.Upon finding out about the large water bill and the running toilet issue, I immediately scheduled a leak detection specialist and plumber to inspect the entirety of the water line and address any found issues at their soonest availability.

Does anyone ever put simple water leak sensors in their rentals to alert tenants with an alarm when there are leaks so they can report them to management? 

These people can have their 'iphones and big screen tvs' to occupy their time instead of breaking into houses or robbing people to put food on the table.

Totally worth it since I bought the place with a leak.

Imagine what that little roof leak turns into ...