It's at 10,000 feet. All modern aircraft are equipped with a toggle in the cockpit so the pilot can turn on & off the seat belt sign. What most people don't know is there are THREE settings. ON, OFF & AUTO. While AUTO is rarely used these days - it's there & set to turn the seat belt sign off at 10,000 & back on again when landing (going thru 10,000). Some airlines still use this (SQ & MH to name a few (as long as the weather is good.

While its PERFECTLY SAFE to NEVER turn your electronic equipment off, the actual rule is 10,000

***For the OP up thread that mentioned he can see that a number if WIFI's are still turned in during take off - its very common for people to turn off their phones & have them turn themselves on again when you put them away. Today's phones are very sensitive and all it takes is the wrong button to rub up against something & voila, your phone is back on......I've never heard if planes falling out of the sky due to this Ill turn mine off only cuz it's a rule for take off & landing but as soon as the wheels are up/down, it goes right back on. There have been more experiments done proving electronics are safe then proving they are not. How does one explain that on EK & a few other airlines I may now make / receive calls during the flight. These are not unsafe airlines, they just don't have civil servants working for the FAA or CAB making up rules to justify a job