Best smart lock for renters that doesn't require installation?

The Level Lock+ is probably your best bet here since it installs inside the door itself rather than on the outside, so your landlord won't even know it's there. It fits inside most standard deadbolts and works with your existing key, so there's basically nothing visible that changes about your door. You control it through your phone or a keypad, and if you ever move, you just pop it back out and reinstall the old lock mechanism. Takes maybe 10 minutes and no special tools beyond a screwdriver.

If you want something even simpler with zero modification to the lock itself, grab a portable smart lock like the Noki or a friction-fit option. These sit over your existing deadbolt and grip it mechanically - sounds weird but they actually work. The trade-off is they're bulkier and look more like an add-on, so you'd need to check with your landlord first. They're decent for short-term situations though, and you take them with you when you leave.

One thing I'd mention: before going all-in on any smart lock, make sure your rental agreement actually allows modifications. Some landlords are fine with inside-the-lock solutions since technically the door itself isn't changed, but others get weird about it. A quick conversation upfront saves you hassle later, and honestly most are cool with something like Level Lock+ once they understand it's fully reversible.