I was in Harbor Freight a while ago and saw a meter with two long probes that go into the soil. It displayed pH, soil moisture, and light level. $7. You may just get what you pay for. I don't know though, I had a more expensive temp/humidity gauge from a grow shop that was so far off on the humidity that it was worthless. Picked up a super cheap one at Harbor Freight, and it works very well. (Maybe I got lucky).