I've got a similar box.
After adjusting the latches so that they would latch tight and reliably, I mounted small flashing LED under the latch handle, a key switch (round key) on the side, and a small battery inside to power it.
Not much in the way of security, but the safest box is the one that a thief doesn't try to open. Neighbors have had break ins, but so far they've passed mine up.
(and it's lots cheaper than the $850 McWelco box I wish I could afford.)
