I am going to look into getting portable alarms for my vacant units.

And after this tenant moves out, just remove it.I learned that when a tenant is viewing an apartment and they ask things like can we add more shelves in the walk-in closet, or darkening curtains because the street light is too bright, or put in hardwood flooring or paint a different color, etc., they will be high-maintenance tenants. 

TBDLaundry Closet: Should I add a bi-fold door here? 

I was debating between a mini split unit, heating/cooling window unit or a portable space heater.

He never worked & getting him out was a nightmare & apparently had his 2 kids sleeping in a closet.

In my experience, this tenant will be someone (from personal real-life examples) will later ask you to put in an extra rod in the already huge walk-in closet because they'd rather have more rod on the wall than the extra space on the end most people like to store boxes in, or they will later ask you for room darkening curtains at your expense because the street lights are too bright, or they decide they want different flooring, or different wall paint or they want in-unit washer/dryers even if your plumbing can't take it in an old building...just on and on and frickin' on.Wishy washy applicants, for me, always, always, always, turned into high-maintenance pains in the rear.So, sure, if you're desperate to get the place rented, and you're willing to deal with whatever is going on with these people that means they need to see your unit again, and don't respect the fact that they're being a pain in the butt already.....then go ahead.But, I'm here to tell you that odds are screaming that these guys will be a PITA, and you will wish you waited to rent to someone else.  

My PM immediately got a portable AC while reporting to home warranty for repairs 2.

(even if they were not on the lease--it's called secret pets).Ask the first responders if they noticed any pets in the unit (via a phone call), and also go over yourself and look around for any hiding under the bed or in closet, etc...Pet food and water bowls in the unit means pets are probably present, and if you don't do this and they die and ROT into the carpet and subfloor you will have one rough smelling rental to deal with.

But they are also ugly, noisy, and expensive to run, so it depends a lot on the class of property and what your goals for the property are in terms of repositioning.It isn't always as simple as just slapping in a central unit; Electrical panel and/or service upgrades are sometimes needed, and you need attic or crawl access for duct work and returns, as well as a place for the air handler to go (which often means giving up a closet). 

I then built a combo closet and pantry in that corner, since the entry door is in the kitchen and we had no coat closet.