One shot for security reasons? (4)

I believe the answer is:

bolt

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'one shot' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for bolt that I've seen before include "Eat (one's food) quickly" , "Find a bar" , "Leg it < and consume apace" , "writer" , "eat food quickly and > lock up" .)

I've seen this clue in the Evening Standard.

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