I would highly recommend buying a cheap analogue hygrometer , i bought one for Rm5.00 .
I have a Aipo Dry Box, fully electronic, but to be on the safe side, in case , i have put the
Analogue Hygrometer in the dry box.
This is just a fail safe so that i have 2 devices monitoring my Dry Box.

Of course you cant beat the Electronic device, but at least i can make out if
everything is working ok...

Just sharing, hope this helps..

it was Best Denki or Denki, the japanese store, that sells cheap stuff..but i checked recently some stores are out of stock..
perhaps you can google and see if others are selling the same..
Cheers