Smoke Alarm Types - NFPA
Buying smoke alarms can be a bit confusing to someone who is not aware of all the different types and the terminology being used. Because of this, I am going to break down some of the most frequently asked questions to help you choose the best alarm. I want to note that there is a difference between a smoke “detector” and a smoke “alarm.”

Installing and maintaining smoke alarms - NFPA
Interconnected smoke alarms increase safety. In a Consumer Product Safety Commission (CPSC) survey of households with any fires, including fires in which the fire department was not called, interconnected smoke alarms were more likely to operate and alert occupants to a fire. 1 People may know about a fire without hearing a smoke alarm.

Learn More About Smoke Alarms - NFPA
Smoke alarms cut the risk of dying in a home fire in half.

Ionization vs photoelectric - NFPA
The two most commonly recognized smoke detection technologies are ionization smoke detection and photoelectric smoke detection.

How To Maintain Smoke Detectors - NFPA
Learn how to properly maintain smoke detectors to ensure safety and compliance with NFPA guidelines.

Smoke Detector Spacing for High Ceiling Spaces - NFPA
This report performs a gap analysis related to the impact of ceiling height and detector spacing on smoke detection performance. Smoke Detector Spacing for High Ceiling Spaces

Smoke Alarms in US Home Fires report - NFPA
This report discusses the presence, operation, and reason for failures of smoke alarms in reported home fires.

Smoke Alarm Troubleshooting - NFPA
If your smoke alarms sound, you should exit the house as soon as possible and follow your home fire escape plan. However, if you keep having nuisance (unwanted) smoke alarms when there is no fire, here are a few things that can help you determine the issue. I also want to note that there is a difference between a smoke detector and a smoke alarm.

Nest Protect Smoke Alarm - Still worth it? : r/Nest - Reddit
I believe currently you can replace a battery detector with a battery detector but you would likely need to upgrade to a wireless interconnect at a minimum. If you pull an electrical permit and plan on rewiring anything, generally they make you fully upgrade to be compliant with the latest electrical code.

Unifi Protect needs smoke alarms : r/Ubiquiti - Reddit
FYI, Smart smoke detectors are dumb. If you want to be code compliant (and actually protected), they need to be replaced every 10 years (lifespan of the radioactive detectors). I don't want to replace $100+ Nest Protects instead of $10 basic smoke detectors. Especially since I have over 10 in my home. $1000 vs $100 is a big difference.