Since I was really bored today I decided to try and see how secure they are. I tried two different "DGT 530" type combo locks in different buildings and each opened in under 5 minutes, probably took this long due to me being a total newb and I'd never ever tried this before. With practice I expect these to "give" in under a minute. Note also that I didn't know the combo in advance and these two locks happened to have 5 digit combinations though I know of others that open with 4 digits.
On a hunch I pressed the C key to reset the lock and twisted the knob clockwise to see if any keys would bind. To my surprise at least one did. This can be felt by gently tapping each key and feeling/listening to the sound. On the first lock, the bound key was really stiff and would not even rattle. On the second lock all keys would give a little rattle when tapped gently so a little more pressure while tapping each key would give me a feel as to which key was bound. As with all lockpicking, this is more of an art than science and it's hard to describe the feeling but I think most of you in the trade should be able to figure it out. It's a matter of how squishy or stiff the key feels to the press I guess.
The whole (obvious) process then is:
1) reset/clear lock with the C key
2) turn knob to apply pressure and identify a bound key
3) release turning pressure on knob and depress bound key
4) repeat from step 2
After 4 or 5 itterations the knob will turn fully and the door will open. The first time I opened the lock I hadn't even kept track of what keys I had pressed so I had to do it all again to identify them
To give you an idea of how cheap and nasty the lock is, the combination doesn't have to be entered in any particular order.
I haven't seen any techniques on the net about opening these particular locks so I hope you guys can have some fun with this.
Cheers
Alex