Residential & Commercial Security - Locks, Keys & Dead Bolts - Single vs. Double Cyclinder, etc...

what's the difference between single vs. double cyclinder? also what's the difference between single vs. double sided keys?

my guess is that double cyclinder should be better, likewise with the keys right? it seems like most double cyclinders are only found in deadbolts.. right?

sorry for the newb questions.. just wanted to get my facts straight.

Double cylinder deadbolts are used where glass can be broken to easily reach the thumbturn and open the door. You have to weigh the security concern versus the safety concern-if you wake in the middle of the night with a fire-how are you going to exit if the door is locked? Good idea to leave the key in the interior lock or next to the door so you do not have to find it in an emergency.

Double sided keys are not always better or more secure. Depends a lot on the construction and bitting of the locks.

thanks for the info.. that's good to know.