https://boingboing.net/2025/01/28/nsa-can-track-powered-down-phones-how-to-actually-protect-your-privacy.html (archive link)

Just want to let you know your cell phone is tracking you regardless if you have it in airplane mode or not. It even ping's when it's turned off. There is only one way to know for sure that you are not being tracked. That's to keep all signals from coming out or going into your devices.

Some relevant issue(s) on GrapheneOS.

Can someone elaborate on whether leaving your device shutdown it contacts cell towers? There are some interesting discussions here https://news.ycombinator.com/item?id=42855678

I think the current approach to protect against it is having the phone always in faraday bag when not in use, and GrapheneOS implement the Airplane-On always mode, enable that feature.

Note: for initial GrapheneOS installation setup on Pixel with stock OS, you will leak some identifiers to cell towers and to google when you enable Wi-Fi for OEM unlocking if your device model is variants (SKUs) which support being sold as locked devices by carriers or when you want to follow GrapheneOS's "best practices" by connecting to Wi-Fi and update stock OS before flashing GrapheneOS.

It's best practice to update the device before installing GrapheneOS to have the latest firmware for connecting the device to the computer and performing the early flashing process. Either way, GrapheneOS flashes the latest firmware early in the installation process.