I was an early adopter of Nest Protect Smoke and CO Alarms. I installed four of them in my house 7-years ago.
Unfortunately, the carbon monoxide alarms expire since their sensors have a limited lifespan. 1st gen Nest Protect has to be replaced after 7 years.
Google is a technology company. They should know something about making an upgrade compatible with previous generations of a product. To my shock and dismay, the mounting hole patterns in Gen 2 Nest Protect are not compatible with Gen 1 mounts. This makes what should have been a super easy replacement essentially a new install.
The Gen 2 Base is on the left.
Shame on you Google. How difficult would it have been to make a base adapter so I didn’t have to drill new holes?