[BMWFamilyMan]

I had an experience a while ago I cannot get out of my mind. I was taking a flight and just prior to lift off the pilot kindly reminded everyone to put their radio transmitting devices in flight mode for the second time (not sure he said so cause they got funky reading from their instruments or not).

I then realized I had my display key with me, and was wondering if it can interfere in some way and should really be equipped with flight mode?

[AP]

Well I would switch it off regardless to save the battery if nothing else.

Not sure when it transmits but it appears to be quite a strong signal as it works for me quite a way away through a couple of floors of my building.
No idea of technically what frequencies it transmits and receive s on or when.

[ADS-UK]

I don't believe Display Key interferes with airplane equipment.

They are so used to asking passengers to turn off devices than any equipment showing interferences at that moment. Acid test is to ask any stewards and pilot friends whether they do the same. I've been told by number of them that there's been plenty of occasions where they've forgotten to turn their own device.

[AP]

I fly a small plane myself and for a phone if left on you can sometimes hear it in the background on the radio but not an issue , just a mild irritation.

I believe if a commercial jet is performing an auto land (ie in fog) they ask for everything to be off just to be on the safe side as the pilots are relying on the equipment to get them down when they can't see anything.