Id advise them maybe, but also you can put up a game cam or a 5G wireless camera from amazon.

I want to install a wireless doorbell for each unit.

If it was a smart meter and you could get a wireless reading, you could theoretically just cut a small opening in a wall, install the meters at points downstream where only one apartment is getting the water, and then patch the wall and collect the monthly usage.

Hi Rosie, I’ve used wireless trail cameras on my properties for security purposes, with good results.They immediately send you text or email photos when triggered.  

Completely wireless and can be monitored/controlled from online.

The Honeywell system with wireless thermostats seemed like a good solution. 

Battery operated so they are completely wireless.

The challenge with these locks is that if you need to terminate or remove a code after the fact you’re SOL: the code duration or use case is locked in and since the “locks don’t talk” back to the Internet there’s no way to remove/change the code after the fact unless you use their local USB stick which acts, similar to a ZWave/wireless SmartHub to sync codes back and forth to another device (like your PC or phone) through the Internet to their system. 

I'm a land use consultant who currently focuses on land use entitlements and lease negotiations on behalf of the wireless telecommunications industry.

The downside to most of these systems is that they are wired (from the DVR to the camera), but they do make wireless versions too.