Hi , I use Weiser Powerbolt2 lock which is just a touch pad electronic dead bolt. As a back up I have a keylock box with a spare key locked to the railing outside the front door with the same key code. If the guest cannot open the Powerbolt lock they can use the key lock box.
Since I live in a low crime area crime area I change the keycodes mabe once a month or if I have a red warning flag when quests check out. Eventually i will install a ring video door bell on the front door to monitor who comes and goes and in case all above fails you can talk the guests through the procedure remotely.
One of problems I find is I leave my front door unlocked most of the times because I live onsite and personally check people in. Guests constantly try to input the code to unlock the unlocked door by reapeatedly smashing the code into the lock which beeps and I can hear it if I am in another part of the house. Total cost of this is around $300 Canadian.
If all else fails there is a doggy door on back yard entrance which I actually had a guest use because they locked the door and didnt take the codes with them when they went skiing.