HUD guidance for ESA does not provide such guidance.A service animal or ESA is supposed to be treated the same as a medical device, like a wheelchair or walker.

All contracts, options, or other devices not based upon a substantial consideration, or that are otherwise employed to permit an unlicensed person to sell, lease, or let real estate, the beneficial title to which has not, in good faith, passed to such party for a substantial consideration, are hereby declared void and ineffective in all cases, suits, or proceedings had or taken under this chapter; however, this section shall not apply to irrevocable gifts, to unconditional contracts to purchase, or to options based upon a substantial consideration actually paid and not subject to any agreements to return or right of return reserved.History.

He now works in a different, but not totally unrelated industry and loves it (medical devices R&D).

An SUV does not include any vehicle that (1) is designed for more than nine individuals in seating rearward of the driver's seat; (2) is equipped with an open cargo area, or a covered box not readily accessible from the passenger compartment, of at least six feet in interior length; or (3) has an integral enclosure, fully enclosing the driver compartment and load carrying device, does not have seating rearward of the drivers seat, and has no body section protruding more than 30 inches ahead of the leading edge of the windshield.

If you have the original key, the small pin-like device, and the new key you want to rekey the lock to.Also there is an app called MyKeyHero.

How does this work once a tenant moves out and added these devices to their phone?

Traditionally I pigtail the wires, but was doing some research online and it seems there is a better option.I found this video about using "colar" device which is a safer approach and safer than pigtailing.

I am a Sr Engineer in the medical device community now and recently acquired an Executive MBA from the University of Memphis.

Also, what OS will you be using on the mobile devices? 

You can only ask for proof that it was prescribed by a physician.As a medical device (similar to a wheelchair) you cannot require extra pet deposit or extra pet rent.