We've have this issue too. We have security keys, that can only be duplicated by registered lock Smiths. As we only have 3 sets (all in use by family members), we are reluctant to hand one over to essentially a stranger. Its not so much the duplication issue, (they should need to provide the correct security code, which they won't have). It's more the lost keys issue. Which would involve a lot of hassle and changing of locks.
Plus, as we are only renting a room in our family home, we stipulate in our house rules, that guests are requested to return by 11pm Sun-Thurs & 12pm Fri-Sat. So hopefully the key issue shouldn't pose too many problems. (We live in a rural area, so not a lot going on round us later than this anyway)!
I have however, considered a smart lock, mostly in case I'm delayed and can't get back in time for check-in, but the type we'd need to replace our current lock, has very, mixed reviews!