Building an Electric Fence Monitor That Alerts You the Moment the Fence Dies
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An electric fence that’s stopped pulsing is just a fence — and livestock work that out fast. The problem isn’t detecting a dead fence; it’s detecting it before you do the morning rounds and find animals where they shouldn’t be.
Here’s the design behind the OGLAS Electric Fence Active sensor — and how you can build one yourself.
The detection principle
You don’t need to wire into the high-voltage side. A small antenna held a few centimetres from the fence wire picks up the induced voltage from each pulse via capacitive coupling. Every pulse triggers a counter. No pulse for N seconds? The fence is down.
This is safer (no galvanic connection to kilovolts), easier to install (zip-tie to a fence post), and immune to the energiser’s voltage level — it either pulses or it doesn’t.
What you need
- Board: Ultra-low-power wireless board — chosen for its minimal deep-sleep current
- Pickup: A few centimetres of wire as an antenna, heatshrinked and pointed at the fence line
- Power: Single 18650 or LiPo cell, with a small solar trickle panel
- Enclosure: IP65 sealed box, magnetically or zip-tied to the post
Why multiple sensors matter
A single sensor at the energiser tells you the charger is working. It doesn’t tell you the far end of the line still has voltage.
For long boundaries, deploy two or three:
| Position | Catches |
|---|---|
| At the charger | Charger / battery faults |
| Quarter-way out | Breaks in the first half |
| Far end | Breaks anywhere, line voltage drop |
Each sensor reports independently with its own node name (fence-east, fence-far), so you know which segment failed — and which paddock to walk to.
Alert immediately, not on schedule
Most sensor systems report on a schedule. “Check in every 5 minutes” means your fence could be down for 4 minutes and 59 seconds before you find out. That’s long enough for cattle to notice.
The OGLAS electric fence sensor reports on schedule and immediately on state change. Fence drops from active to inactive? Message fires right now, not at the next interval. The bell in the homestead rings the moment the alert lands.
Battery life that matters
The sensor sleeps between pulses. Wake, check for a pulse, update the counter, sleep. Full power-down of the radio and the GPS between cycles. The whole active cycle is under a second per check.
On ultra-low-power hardware with a 2000 mAh cell and a small solar panel, it’ll run for a full season without attention — and reports its own battery voltage so you can swap before it dies.
OGLAS electric fence sensors are part of the sensor catalogue. If you’ve got a long boundary and a story about stock getting through, we’d like to hear it.