Hidden Pressure Plates

There are different kind of secret triggers in minecraft:

Entity movement

Living entities like animals and monsters can only move if a player is in a 32 block radius, this radius is a spheroidal box around the cow. By placing the a cow in a place where pistons keep pushing the cow back you can make a proximity detector.

This can be seen at:

Tripwire

If properly applied, tripwires are hard to see, this works the best if the tripwire is placed around the eye level in buildings, or at the feet in the outside world.

Hidden pressure place

Its also possible to make a pressure plate completely hidden, for example, stone pressure plates can be nicely hidden in a hallway that goes down, the following image demonstrates this:

Did you see the pressure plate at the end of the stair?

Block update detector based detection

Some blocks have a special property that they update when the player walks over them, for example, redstone ore blocks start glowing. This can be detected with a BUD to deliver a redstone signal. A simple implementation this looks like:

The item through a corner technique

Items can be pickup through the corners of the blocks, by making your player pass past such corner, you can detect it using a wooden pressure plate in combination with a torch.

The casual player technique

What if you didn't need to make a hidden trap? You could add a couple of iron doors in combination with buttons to your building, this way the player going through it will thrust the button to continue, and keeps pressing them to open the next door.

The trapped chest

By placing a large number of loot crates through your building, player will get blind opening chests, they will just open every chest to get a little loot. By making the trap have a trapped chest in combination with some delay, the player will suspect nothing.

The minecart in a corner

Like items, you can also interact with minecarts in corners, by combining this with a powered rail and a detector rail, you have a accurate corner touch detector.

Command blocks

If you are making a custom map, you can also use command blocks for this purpose. You can run the command testfor @a[r=4] from the commandblock in a loop using a clock, then check the output using a comparator. If you want a other center then the command block, there are 2 ways that you can do:

• Use the @a selector with x, y, z argument: testfor @a[r=4,x=X,y=Y,z=Z]
• Place an armorstand at the required location and use execute @e[type=ArmorStand] ~ ~ ~ testfor @a[r=4], you can give it a name and address it that way if you use this trick in multiple locations.

If you feel like using the modded approach, the Secret Rooms Mod should help you out. It adds a variety of hidden blocks such as pressure plates, levers, one-way glass and walk-through blocks.

The mod can be found on the Minecraft Forum.