Yea the lithium-ion batteries are pretty good, you can also get 10 year smoke detectors with a built in lithium battery. Also a psa, smoke detectors usually only last 10 years and need to be replaced after that. There’s often an expiry date on the detectors.
The battery in smoke detectors should be changed every year and you should ideally test the detectors using the little button monthly.
In Norway we have an official smoke detector day which is on December 1. where we’re supposed to change the batteries. Its because Christmas is the high season for house fires.
I have a TP-link Tapo D230S1. It comes with an indoor chime that acts like a hub that has an sd-card slot. The hub supports up to 4 compatible cameras and 64 other devices. It’s also pretty affordable and easy to set up. It is however battery only, but it lasts for several months between charges.
I don’t know of any smart doorbells that can also open doors. Maybe you could use a shelly relay or something similar?
Lithium batteries last 5-10 years, regular 9v alkaline batteries last about 12-18 months. Some sources recommend changing the batteries every 6th month but i personally think that’s a bit excessive.
I only have a small 2 room apartment so i just got myself a cheap-ish optical smoke detector with a built in lithium battery. The battery should last 10 years which is how long smoke detectors last before they should be replaced.