safety lock vs safety device

safety lock and safety device both are nouns.

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

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

safety lock: guard consisting of a locking device that prevents a weapon from being fired
safety device: a device designed to prevent injury or accidents

Other hypernyms of safety lock include guard, safety.

safety lock (noun)	safety device (noun)
guard consisting of a locking device that prevents a weapon from being fired	a device designed to prevent injury or accidents
a bolt that cannot be moved from outside the door or gate