This instrument monitors ambient radiation in large areas within a range of 0 to 4,500 mRhr. Area monitors like this have outer (2cfb4eb2-68db-4d07-b387-f9bffd81e0de)

A square silver object with a dial that points to X1. Beside it is also X10 and X100. There is a box with four zeros. There is a switch and several circles with glass. The number 12 is handwritten on what looks like tape.
This instrument monitors ambient radiation in large areas within a range of 0 to 4,500 mR/hr. Area monitors like this have outer casings to protect the inner Geiger-Mueller tube and electronics. Workers set this device on the floor to monitor radiation levels. It emits an audible alarm when the radiation levels become dangerous.