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How Do I Prepare My Phone for a Protest?
(themarkup.org)
This is a most excellent place for technology news and articles.
Most modern devices track the phone even when it's turned off. If you can't remove the battery, leave it at home.
When I shut the lid on my work computer I assumed it was "off" or at least inactive. My home network showed me it was continuing to "check in" throughout the night.
Closing the lid typically does sleep or hibernate, both of which can still be active. I've had many windows updates overnight with the lid closed.