Secured premium notes are issued with the warrant which is kind of detached. This can be redeemed after a notice period of 4-7 years. This way it ensures the holder right to apply and get the allotted equity shares. Secured premium notes has lock-in periods during which the interest is not necessarily to be paid for the invested amount. It also has many options to do the sell back to the holders at par or face value after the lock-in period. As in this only it contains lots of risks as the holder gets one equity share after a fixed period of time.