I was an early user of "unnamed" popular Kickstarter door lock and I took my dog out at 9pm and came back to find that the batteries were dead.

I called the customer support and they told me the low battery alert message was sent after I had locked the door and left, which was about a 20 minute trip.

They ended up paying for my locksmith, but I haven't felt comfortable using the lock since so it just sits on my door.

Wow, so it predicted its battery was low less than 20 minutes before it died? That's awful.

My current apartment has a "smart lock" system for entry into the building. The system becomes unresponsive with no electricity, which means you're locked out.

But you can kick open the door anyways, so at least that's an alternative to being locked out.

In my apartment building all of the external access doors are held closed by electromagnetic "locks" that require a key fob to open, unless we lose power, in which case there's no battery backup and they're all unlocked.

Jesus, what if that failed in a fire?

In the case of a fire tenents try to get out of the house and usually there is a normal manual turn lock on the inside of the door that works without electricity.

For the fire fighters, I assume they break down the door anyways?

Nearly all smart locks can be mechanically unlocked from the inside (as required by fire safety regulations).

Add "or the manufacturer decides to deactiveate the servers on which the locks are dependent and the email informing landlord winds up in the spam folder" to the mix.

I just recently had this happen to me and I did get locked out when the battery in the lock died. It happened at 11 at night when I came back from a long trip and my landlord was not responding to calls. After about 10 minutes of Googling I figured out that there are 2 prongs at the bottom of the lock that you can connect a 9-volt battery to to give the lock temporary source of power. I went out and got a 9v battery and unlocked the door with my fob while holding the battery terminals on the 2 prongs.

I guess it's better than nothing but that still sounds awful...

Any GOOD smart lock that you'd want to put on your house will have key backup. You basically have to be a complete douche to install a keyless system in a residential application.