[eqvinox]

Containers aren't really a uniform thing aside from their size and stacking. Whoever commissioned/owns the container could decide to put a tracker in, but to my knowledge (which is from "hobby curiosity") it's extremely rare.

Also, the GPS trackers would stop working very quickly if the containers sink. Regular bulk shipping containers aren't waterproof so I'd expect the majority of the lost containers to be at the bottom of the ocean by now - at that point the trackers would neither receive GPS nor be able to send anything really. (cf. https://en.wikipedia.org/wiki/Communication_with_submarines )