Keep the radius search, but add two additional checks before it explodes.
First, make sure the player is in front of the claymore. You can do this by seeing if the dot product of the forward vector of the claymore, and the direction to the player from the claymore, is more/less (not sure, experiment a little) than a certain threshold. The dot product should go from 0 to 1 depending on the angles (assuming both vectors have a length of one).
Second, send a raycast from the claymore to the target, to make sure no bricks are in the way. I recommend using getHackPosition of the target to get the center of the player object.
You can find out how to do both of these by searching the coding help board. For the first one, search for "can see", and use code for checking whether a player can see another object, and modify it for your own use.