The Oxford Alarm-D U-Lock Pro is a thieves worst nightmare. With a Silver Sold Secure rating the lock provides the one of the highest standard of security for your bike. The shackle of the lock is constructed with 14mm Hardened Steel and is accompanied by an unnaturally loud, a 120dB alarm which is activated when the lock is disturbed. You have the option to activate the alarm when you are locking your bike. Simply turn the key once and you'll hear one beep which means the alarm is activated. To deactivated the alarm, but still secure the lock, turn then the key once then back to the start, then turn the key again, this will produce two beeps which means the alarm is deactivated The weatherproof alarm is powered by a long life lithium battery and has an output of 120 dB, which is at a similar level to the siren on a fire engine or a chain saw. With a high tech, pick-resistant locking system, it will be very difficult to infiltrate this lock.