You don't need a taser. You can immobilize the birds by utilizing a built-in mechanism that Mother Nature gave them called "Tonic Immobility." Some people call this "hypnotizing" or "Trancing" the chicken.
Pick up the chicken and hold it on it's back in your arms, holding the wings and stroke it's breast. It will eventually go still and LOOK like it's asleep. What's actually going on is the chicken is still awake and aware, but they have had a rush of serotonin (the feel-good "happy" chemical that our brains use to regulate mood) to the brain, and it makes them go still and limp. This allows them either to avoid being seen by predators, become uninteresting to predators, or not suffer as terribly if they are eaten anyway.
Anyway, it allows you to kill the bird easily and quickly with minimal fuss, and they don't know what happens or suffer. I use this since I normally don't slaughter a whole bunch of chickens at one time. Since the chicken is relaxed, it's easy for them to bleed out and the feathers pretty much fall out after a good dunk in a pot of hot water. MUCH easier to pluck.