How to make lock down trap in minecraft

first, you will need to dig 8 x 3 space and 2 blocks deep. make an extra space with 3 x 1 and 2 blocks deep on top left corner like so.

this is where the entrance is going to be. place any block at bottom and place a flooring material 3 blocks next to each other like so.

place an iron door at middle and place a redstone torch where you can see little bit where my pointer is. place door first and then place torch underneath.

behind of the block where you placed torch, make a redstone clock and connect to block

behind a clock, place block of your choice like so and place redstone dust right there

place a repeater and dust and connect it to clock

place a trapped chest at the top of redstone dust one we placed on step 5.

cover up the floor and wall with your block of you choice

and, build a sealing. its all set!

in order to reset trap (after someone got trapped in) you will have to go to extra 1 row at the end and replace a redstonedust on clock

once someone open chest, door will close and he/she will get trapped!