How high do drones fly?
Modified or in "error" mode : as high as the battery will take them.
An anecdote heard during a recent UAS symposium : F/O of well known European airline buys a high end drone for around 1000 USD in Bangkok.
He wants to try it near hotel pool before taking it home. The thing shoots up vertically and is unresponsive to the ( possibly incorrect) iPad commands. It climbs until out of sight ...stuck it its vertical climb mode. Never to be seen again ..
And yes, it is only a matter of time unfortunately...