Start work to study adopting security measure (5,2)

I believe the answer is:

clock on

'start work' is the definition.
(to register arrival at the workplace)

'study adopting security measure' is the wordplay.
'study' becomes 'con' (I've seen this before).
'adopting' indicates putting letters inside.
'security measure' becomes 'lock'.
'con' going around 'lock' is 'CLOCK ON'.

'to' acts as a link.

(Another definition for clock on that I've seen is " Arrive for work".)

I've seen this clue in The Times.

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