If the lock is a single-cylinder deadbolt and the knob inside the door is accessible turning the knob opens the lock. If the lock is a double-cylinder lock or the inside of the door is not accessible, special lock picking tools are necessary. If the deadbolt is not fully locked into position, pressing a credit card or other flat tool into the space left by the partially opened deadbolt allows it to open. Completely locked deadbolts require special lock picking tools to open.
Common lock picking tools include metal picks and a tension wrench. While picks are specialized tools, a flathead screwdriver can be used as a tension wrench because they are readily available. Common metal objects such as paper clips can be bent into picks for a specific type of lock. Some locksmiths use electric pick guns instead of a traditional pick and tension wrench. A pick gun has several different pick-shaped tips, which vibrate to push the pins of the deadbolt lock up.
While there are many legitimate reasons to pick a lock, possessing or using lock-picking tools without a license is illegal in some jurisdictions. In California, for example, it is a misdemeanor to possess a lock pick without a locksmith's license. Always check local laws, and call a licensed and bonded locksmith if there is any doubt.