normieprivacy
Airplane mode only controls what the phone's software transmits, but has no effect on what its physical structure reflects. Even if the phone is physically turned off, it will still reflect waves from the surrounding environment and announce its presence. NSA TAO tools reveal more sophisticated applications, such as LOUDAUTO or TAWDRYYARD (these are rather old tools). On a slightly different but related note, a Wi-Fi modem was also supposed to be harmless, and today, for example, Comcast offers a Wi-Fi sensing service called Wi-Fi Motion (Xfinity Shield). It's so accurate that you can specify that home motion scanning ignore, for example, a cat or dog. This allows Comcast to detect whether you're home or alone, where you are, and what you're doing. Comcast informs you that it may share this information with third parties, including law enforcement. Even if you don't physically have their modem, your neighbor might, and their modem will report whether and how much time you spend at home. I hope this sheds some light on the issue of radio waves, for which Faraday cages are one of the methods of protection.