eRentalLock.com has the best solution.
I have used it since 2013.
It doesn't use Wi-Fi.
You buy it online and install.
After the initial purchase there are no other fees.
They also have great tech support.
HOW IT WORKS:
This company from Canada buys Schlage Locks and modifies them to work with their software.
Guests get a 10 digit code that they can reset to a 3 or 4 digit code for their stay. No Keys Needed.
The lock has a battery and knows its serial number and date/time.
From that it can look at the 10 digit code and determin the start and stop times.
The lock will only open between those times.
The lock comes with regular keys so I have one and the bulding manager has one.
HOW I USE IT:
When someone books I ask for their personal email so I can send them a 10-digit code for the front door.
I log on to the web site or on my downloaded phone app.
I enter the Name and arrival and departure dates and times.
A document is created with the 10-digit code and pre-written Lock instructions that I have modified with my own comments.
At the top of the document is an "email" button. I put in the persons email and it is sent to them.
On the software I can also see a listing of every person who has had a code.
This is a great way for me to keep track of my guests and also my cleaning crew or workers.
I make a 2 year code for myself so my family never needs a key.
ADDED SECURITY:
There is a USB thumb drive in the lock that records every time the door is opened and closed and with which codes.
You can open the lock (like when you change the battery every year or so) put the thumb drive into your pc and look at the data.
If you had an incident and needed to prove who was going in and out then this would be hard proof.