[lumiukko]

and he didn't think to turn off his speaker after the flight crew requested all BT devices to be turned off repeatedly?

or was it one of those in-ear headphones that are borderline impossible to turn off when outside of their case?

[victorbjorklund]

It was in the luggage compartment. Even if he had thought about it he probably would not.

[Cyan488]

I wonder if the speaker had built in lithium batteries too.

[simulator5g]

Devices with built-in batteries are ok for checked bags in the US (though, the temperature swing isn't good for their long term health, and whichever airline you choose may have their own further restriction on that). It's just removable batteries that must be removed.