An alternative to a key ring (3)
I believe the answer is:
orb
'ring' is the definition.
(I've seen this before)
'an alternative to a key' is the wordplay.
'an alternative' becomes 'or'.
'to a key' becomes 'b' (eg B major, musical key).
'or'+'b'='ORB'
(Other definitions for orb that I've seen before include "Ring" , "A sphere or globe" , "Part of royal regalia" , "Ceremonial globe carried by a monarch" , "component of royal regalia" .)