On 26 Feb 2021 at 09:27:53 GMT, "Harry Bloomfield, Esq."
wrote:

Robin formulated the question :
How does that detect a failure of an infrared transmitter?

It doesn't, it will detect a radio remote control's operation. For IR,
point it at a camera, or camera phone and look at the resultant
picture.

A convenience, that applies to our satellite box but I'm not sure about its
Human predecessor, is an LED on the target equipment that flashes when it
receives an IR signal. It is useful to distinguish a remote control failure
from the satellite box itself locking up, which latter is annoyingly common.

--
Roger Hayter