NASA's method to detect hydrogen fires was to “hold out a broom in front of you”

> Previously, firefighters responding to a hydrogen fire had to give the suspect area "the broom test" by carefully probing the suspect area with a corn straw broom to determine the presence and location of a fire. This technique has significant safety and accuracy shortfalls,

The technique is however a vast improvement over the previous method: finding invisible flames with one's meaty parts.

The humble stick is still an important sensor for many applications. Checking for leaks in Diesel fuel systems and hydraulic lines also leaps to mind. It's one of those technologies that's really hard to improve on.

Fairly sure that's a common thing in all industries that work with non-trivial amounts of hydrogen.