I have two different kinds. One is a stand alone digital temp/humity one for like 20 dollars. The other is a LaCross or Oregon Scientific with remote indicators. You know the ones you put a sensor outside and see the temp remotely inside. I just bought an extra sensor as it can handle 4 or something like that. I put it directly in the safe. My humity before was like70% in spring time peak.Now, i never let it get over 45%.

Same thing in my reloading room. I had to buy a dehumidifyer. Made a world of difference.