another good replacement for the credit card or butter knife is a paint scraper
you can make this an even better tool by using a bench grinder to cut a C-shape into the side with about 3/4 of an inch to the end. that way you can get inside to the front part of the metal piece that goes into the lock plate. this tool works on many doors that wont open to the card or knife.
another interesting way of getting into doors sounds crazy but it can get around door bolts fairly easy and no normal door lock has a chance.
materials:
1 standard screw-type car jack
1 length of 4"x4" approximately 2.4 feet long
directions:
at door knob level, (if no bolt) or at bolt level if present, span the doorway with the 4x4 and the car jack expanded to cross the doorway. slowly open the car jack and the doorway will expand so that the bolt or generic lock will no longer be inside its lockplate. this way is fairly traceable because the jack and board will leave marks on the doorway, you can bypass this effect or at least minimize this by using 2 pieces of 2"x4" about 1 foot in length to distribute the pressure over a greater area on both sides of the doorway.
if you really want to be professional and FAST use a pneumatic oil jack and premade boards screwed into a T-shape for one side and zip strip the 2x4 to the jack.
i hope someone finds this information terribly disturbing and see their world for the illusion it is.
there is also a tool you can make with metal rods and interchangeable hooks and leather straps to go under the door and manipulate the locks from the inside. the one i made uses a laser pointer to show you within inches of where the tool is on the other side of the door. this works great at hotels and if you dont want to damage the lock/doorway/ect ill save this tool for a diffferent post
regards
tecvoid