I agree with JWP, it is only polite to pay attention to the safety briefing, although like the seatbelt sign, on many US airlines, it seems to be optional.
I'm well aware of why electronic equipment should be switched off for T/O and landing, and why no radio transmitters should be used in flight. But with modern hearing aids, pacemakers, insulin pumps and other implants, it may not be possible. Fortunately, the powers are so low that interference to A/C systems is improbable. I suspect ICAO haven't caught on yet to the fact that these devices have transmitters in them: it took them some time to classify pacemakers as hazardous cargo because of some in the early 1980s with plutonium batteries. There have been none of those manufactured for at least twenty years, but pacemakers are still classed as hazardous cargo.