I can get phone records of the subject, their friends and family, employers, address history, land lines, cell phones, judgements for 2 dollars a search and then full blow background checks for tenant screening for 12 dollars. 

Occupant profile: two older ladies on SS, one with mental disability and another with cancer undergoing radiation treatment.

Or you taking all those tire kicker calls on your cell #

The ability to do this easily and securely is also important.Finally, controlling all these two-way systems from anywhere in the world with internet access or a cell phone signal is a given, but control of all from ONE app has been the latest challenge.

The duplex I bought that cashflowed was 63k and it was a guy who had cancer who needed to sell quick.  

I got into this situation because we have never used outside funding, we have only used profit from our other properties to fund rehab, but due to round 3 with cancer we had to put it on the back burner for a short period of time.

Forward the calls to your cell phone.

Also - " Smile , Keep Eye Contact, (no sun glasses), keep your hands and arms open, turn a quarter or half turn so your back is to the front door as it opens, (Smile and stretch your arms out open in your car just before you knock), stay positive, always be closing for appointment, set appointment for future date, get phone # and cell #, bring paperwork to appointment, ask questions as to what is the most important issue with selling this home, craft your pitch around this answer, close deal, repeat process for next deal "Door Knocking in a nut shell ...You will strike out say 9 out 10 times, so what?! 

Alarm system runs off cell towers; no need for a landline. 

When they do, get their name, email, and cell number.