However, there are smaller items that seem so trivial that can hold up the financing such as a water heater not strapped to the wall, a broken window, missing fire/CO alarms, etc.   

Install a water meter alarm, it hooks up to a phone line dials up number if it senses a continuous use of water so the property can be checked.You need an addendum to lease that specifies that heat needs to be kept at 68 degrees or tenant will drain lines and shut off water if property is left for long period of time.If this would have happened in a upstairs bathroom / frozen pipe / you could have really had serious damage. 

@Peace Lily More alarm bells should be ringing in your head.  

Could please someone recommend what I should do if my tenant's smoke alarms frequently (once in 1-2 months) go off for no apparent reason?

If such maintenance is costing you 150 a month,it must be a very big pool, anyway, I suggest you;Make out written instructions about the maintenace of a pool and make it part of the lease.Set rents without consideration concerning the poolRequire the tenant to have renters coverage with liability covering the pool in addition to yours.give them instruction until you are satisfied.give them an emergency number for a pool guy along with other emergency numbersensure the pool meets all safety ordinances applicable to the property and require the tenants to care for alarm equipmentI assume utilities are in thier nameNow, maintenance of a property is an owner responsibility generally by law or custom, pass it by your attorney!

I also lock exterior A/C circuit boxes and label the units, cage and circuit box with A/C specific alarm stickers that I had made up.I will frequently install an inexpensive alarm system (not monitored) which gives me peace of mind between tenants and acts as a selling point when showing the units.I've doubled up on door stops (to prevent doorknobs from going into walls).

We have been working reminding the police on a regular basis to patrol our area more, and have installed a Simplisafe alarm system. 

This allowed the smoke to come in and set off the alarm and wake himup probably saving a heck of a lot more damage. 

What if the prospect turned out to be a thief?

They also have some strict laws about smoke alarms everywhere (there are 6 required in one of our houses with only 1300 sqft - unbelievably loud during testing), and carbon monoxide detectors on each floor.