Concentrates when safety devices get old and cold (7)
I believe the answer is:
focuses
'concentrates' is the definition.
('focus' can be a synonym of 'concentrate')
'devices get old and cold' is the wordplay.
'devices' becomes 'fuses' (fuse is a kind of device).
'get' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'and' means one lot of letters go next to another.
'cold' becomes 'C' (abbreviation, eg on taps).
'o'+'c'='oc'
'fuses' going around 'oc' is 'FOCUSES'.
'when safety' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Another definition for focuses that I've seen is " Concentrates".)