warning device vs device

warning device and device both are nouns.

Word	Noun	Adjective	Verb	Adverb
warning device	Yes	No	No	No
device	Yes	No	No	No

As nouns, device is a hypernym of warning device; that is, device is a word with a broader meaning than warning device:

warning device: a device that signals the occurrence of some undesirable event
device: an instrumentality invented for a particular purpose

warning device (noun)	device (noun)
a device that signals the occurrence of some undesirable event	any clever maneuver
	an instrumentality invented for a particular purpose
	an emblematic design (especially in heraldry)
	any ornamental pattern or design (as in embroidery)
	something in an artistic work designed to achieve a particular effect