I’ve bought the Nest for our unit ($279). It’s all wifi driven with a nice smart phone app. It notifies you when it’s unlocked and who unlocked it, based on the code. You can set start and expire date/times. You can set operational times (so your cleaners can only access unit from say 12PM to 4PM). You can lock remotely if you see it was left unlocked.
I have not actually started hosting yet, and I’m worried it may prove a little complicated. You have to touch it to start, then key in number, then hit the check box. Not huge, but from what I’ve been reading in these forums, I’m concerned about technophobes.