Secret number initially protected at home (3)
I believe the answer is:
pin
'secret number' is the definition.
'pin' can be an answer for 'number' (I've seen this before). I am not certain of the 'secret' bit.
'initially protected at home' is the wordplay.
'initially' indicates taking the first letters.
'at' says to put letters next to each other.
'home' becomes 'in' ('he's home' can mean 'he's in').
The first letter of 'protected' is 'p'.
'p'+'in'='PIN'
Can you help me to learn more?
(Other definitions for pin that I've seen before include "Peg or nail" , "Fasten; a security code" , "Debit-card number" , "form of identification" , "leg" .)