Removing these items from the vents solved the issue.In one other instance the complaint of a unit not coming on was solved when we replaced the dead batteries in the thermostat. 

Or sand the floor to recondition this would indicate you can take the deposit to fix the damage areas.

It is battery operated and can be secured in many ways.

My guess is that the roof is flat; and solar panels should be angled a bit facing south I believe, so you might have to add some structure for that; then you would need an inverter, and you might even want a bank of batteries for storage (and maybe not since you can sell excess generated electricity back to PECO).

Rent could be raised some however and with reconditioning the inside they could be raised a little bit more - All units are currently rented and there is a good setup of automatic payment and none of them have been late on rent.  

I also inspect plumbing to assure there aren't any leaks, maybe filter replacement, co and smoke batteries.

It's also critical to tell your tenants if that alarm starts going off, don't just pull the batteries.

I've looked into this and found an interesting read about how Tesla/Solar City is a threat to utilities because you can use a Solar Roof/Solar City installation and a Tesla Powerwall battery to store excess energy and sell it back to utilties.

The vendor will then contact you directly to schedule a time for service.If for some reason you don't have access to your online portal, you can call our main office, hit the prompt for maintenance and then you will be automatically directed to our 24 hour maintenance team.Just a reminder regarding maintenance, that AC Filters should be changed every thirty days, and smoke detector batteries should be changed at least once a year.Your new home has been professionally inspected prior to you taking occupancy, and a copy will be sent to you once received from the inspector.

@Quynh-Chi Nguyen,Contact the company, and ask them to send you a replacement cover, i'm guessing it was making a noise and they removed the batteries-- can you ask them if they know where it is?