safety device vs device

safety device and device both are nouns.

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

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

safety device (noun)	device (noun)
a device designed to prevent injury or accidents	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