Earlier quoted context omitted.
Most leases will explicitly require the landlord have unfettered access to the property. Usually, the only caveat being that the tenant will be given some amount of notice. My leases say 24 hours. /If I ever came to one of my properties and my key didn't work, you better bet you'd be evicted.
I see two options: 1) You announce before 24h, and therefore the renter can lend you a set of keys 2) You come unannounced. If it's an emergency you can break the door. If it's not then you've got no business being there.
On your greater point, there are a million ways to skin a Roman senator. There are alternatives that don't require a smartlock and if an otherwise great tenant (or applicant) really pressed the issue, perhaps I'd go with another one. In the absence of that, I'll go with what's easiest and sensibly secure (which, by the by, a smartlock is).