The hay moisture probe
The oldest fire on the frontier, prevented by a stick with a meter on it.
What it is
A long-stem probe pushed into a bale or into the stack, reading moisture content. Paired, if you put up much hay, with a few temperature spears left standing in the stack and reporting to the house.
The numbers
- Hay baled above roughly 20% moisture (lower for large bales — closer to 16–18%) can self-heat.
- 150°F internal means check it twice a day. 175°F and climbing means get it apart or get help.
- Above roughly 190–200°F you are into the range where hay fires start on their own, with no spark and no cigarette.
- Probe cost: $50–150. Barn cost: ask your insurer.
Why it's here
Wet-stacked hay burns barns down every single year, in every state, and it does it from the inside of the stack where nobody is looking. This is a case where a cheap instrument replaces a judgment that even experienced people get wrong, because the thing being judged is invisible.
The automation angle
The probe tells you before you stack. Temperature spears wired to the house tell you after. Rising core temperature is the entire signal — and unlike almost every other alert on a farm, this one is worth waking up for.
The catch
A probe is a point reading. One dry sample doesn't clear a whole load, and the wet spot is usually the one you didn't test — the windrow that sat in the shade of the tree line. Test the part you're least sure about.