There are many types of locks to choose from for securing a bike while it’s parked. Some, like cable locks, are light weight and easy to transport, but might be easy to break.
Very heavy weight bike locks might be best stored on the rack where the bike is parked the most, such as the rack outside work, a dorm or apartment.
Bicycle Cable Locks: Are They Good Enough?
Cable and chain locks are popular choices, but are actually very flimsy and any serious thief will be able to cut through them with minimal effort.