Basically a JVS brick then when hit with a key, makes the lock go away.
I modeled my own to see how it would look.

(The second "Unlocked" one is just me moving the top thing up to show what it would do.)From the model, when the key hits the lock, the gears will turn, the top part will pop up, and the lock will fall off and disappear thus letting you open the door.
I need an animator/scripter (
Idea ripped from Zelda Games)
As to what it should be attached to, I'm not sure yet. Chains, a bar, the door handle itself, I really don't know.
Model Link Here(
Includes DTS, MS3D, and texture files)
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I made a key suitable for the Gear Lock. The Gear Key

Made bacause the default keys Badspot made, just wont cut the mustard.
Model Link Here(
Includes DTS, MS3D, and texture files)
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New Lock! Pad Lock. Perfect for any normal locking needs.

Has same loop attachment as the other Lock.
Model Link Here(
Includes DTS, MS3D, and texture files)
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Normal Key, For the normal Lock above.

Yea, Just a basic key.
Model Link Here(
Includes DTS, MS3D, and texture files)
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Also a Card Key lock that I just recently modeled.
Hit with a card key (
Soon will be modeled), it accepted green light will flash, you can add your own sound or something hence the little speaker.
If failed the red light flashes and doesn't let you through.
Simple concept.
Model Link Here(
Also includes DTS, MS3D, and texture files)
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Card Key, to go with the Card key lock.

Nice and simple.
Model Link Here(
Again, includes DTS, MS3D, and texture files)