hi guys, the latest and most reliable keyless entry system is from ISEO.
the LIBRA electronic cylinders can be retrofitted to most existing locks and you can forget the keys forever.
I use one in my property and even put one in my own house.
the installation takes less than 5 minutes(if retroffiting).
through the ISEO app you can send a text or email to the guest from anywhere in the world.
the text contains links that will first download a free app and secondly it will use that app to open the door.
Before & after the predetermined date and time the guests phone will no longer open the door.
The batteries will last 3-4 years.
cheers.
danny