There is nothing like a "mold meter". There are mold test kits available at some big box stores. You need to be very cautious in how you use them. Most will find mold just about everywhere which is pretty accurate since mold spores are just about everywhere. Especially in a home. If you were outside mulching your flowers or mowing the lawn and walked into your house, you just introduced a bunch of mold spores to the inside. Open a loaf of moldy bread on the kitchen counter and you release loads of spores into the air. Odds are they will pretty much stay in your house floating around in the air. Mold spores can stay airborne for months in a noramlly used room. Even opening a bottle of ranch dressing will introduce mold spores to the air. There are documented cases of mold remediation techs messing up air samples by eating lunch in the same room where the clearance tests were being conducted. There are some ways to test for mold, all of which involve sending samples to labs. There are Particulate counters that will register the number of particles for a given volume of air. Those particles could be mold spores or dust or practically anything. There are also moisture meters that will supply the quantity of moisture in a type of building material. All of these are tools that a true professional will use to determine if conditions are right for mold spores to generate into mold colonies. Mis-use of any will provide information that is inaccurate and could cause you to make some very costly decisions. The best "mold meter" are your 2 eyes along with some common sense.