A hundred security devices -- tickers? (6)
I believe the answer is:
clocks
'tickers?' is the definition.
(things which tick)
'a hundred security devices' is the wordplay.
'a hundred' becomes 'c' (roman numeral).
'security devices' becomes 'locks'.
'c'+'locks'='CLOCKS'
(Other definitions for clocks that I've seen before include "Timers" , "Notices" , "Timepieces" .)