@Rob Cee I've owned these for 10 years. Really not much has changed in the last year I've lived out of state -- with the exception that I absolutely have to have local people I can trust who can check in on things and let me know when something is wrong.
Fortunately my tenants are great. Most have been with me for years. I keep rents low, provide free wifi and cable, and so turnover is very low. I think turnover is the most difficult aspect of remote management. The e-locks will help this a bit, but nothing compares to being on site to show your own unit.
@Jay Hinrichs I would say I have B-level rentals; modestly updated, but in 'transitional' neighborhoods, and old buildings. The tenant checking accounts are essential. If you can't write me a check for a deposit+rent, then I don't trust you're financially stable enough to rent from me. I do not accept cash at all, and will only accept M.O. or check on a limited basis (I can deposit these with a cellphone photo if absolutely necessary). Ultimately everyone pays electronically.
I understand if you're doing HUD housing this may not be as easy, but in my experience spending 15 minutes with a tenant and showing them how the app works saves everyone time in the long run.