We've started relying a lot on electric fences, and as the fences have grown, they've gotten a lot more complicated to troubleshoot when there's a problem. I've used one of those cheap 5-light neon testers for a while. To use them, you just push the ground probe into the dirt and place the tip against the hot wire and when the charger pulses, it lights up a number of neon lights to give an indication of the voltage range... like between 2500-3000 volts. That's it.
Here are the problems with that kind of tester...
1. The neon lights can be hard to see in the daylight.
2. If your voltage is really low (below the range of the first light), is it working at all? Or, is it just a little low? (A quick grab of the wire will tell you. But sometimes, it sucks to be the one grabbing the wire).
3. Pushing the ground probe into the ground is a pain in the butt if you're trying to find a fault and having to check a lot of different points.
I finally gave in and purchased a Gallagher Smartfix for about 99 bucks.
If you just want a quick check of the voltage to make sure the energizer is working, just lay the wire across the sensor and look at the display. It turns on when it senses a pulse (showing a little lightning bolt) and gives a digital readout of the voltage. A quick press of the mode button will show if there is any current flow (which indicates that there is a "leak" in the wire). For better accuracy, you can place your thumb on a little nub and it will use you as the ground (and you won't get shocked doing it). For the best accuracy, you can still plug in a ground probe into the dirt and get a measure of what an animal will feel if it crosses the wire.
In current mode, if it displays a current reading (which indicates a fault in the circuit), it will display an arrow showing which way the current is flowing (and which direction to search for the problem).
In testing it, I measured the voltage out of a small solar energizer and it read 5.2 kV just laying on the wire, about 6 kV with my thumb on the nub, and about 6.5 kV when it took my foot out of my shoe and put it directly on the wet grass. Since I consider 3 kV to be about the minimum effective voltage, I didn't feel the need to put in the ground probe. I switched it to current mode and it read 0.0 amps. So, I know that I didn't have any faults in the electric net that I was testing.
For testing in tight spaces, it has a little pop-out probe that can reach into switch contacts and spots like that, with less accuracy.
I like being able to get an accurate reading, instead of a range. It gives me a better idea of how much my fence voltage changes with ground wetness (dry ground will greatly reduce the shock given the animal and may render the fence ineffective if the animal decides to "try it".)
All in all, I'm loving this little gizmo...http://www.gallagherusa.com/electric-fencing/permanent.component.aspx?mktprodid=1358