In the past, training collars were limited in the ability to adjust the intensity of the electronic stimulus and were often referred to as shock collars, which gave them a negative reputation. Modern remote training collars feature a signal that can be used before electronic stimulation is applied, to alert the dog and act as a warning that a behavior such as 'stop' or 'sit and stay' is required before electronic stimulation will occur, and simulation itself is adjustable so that it can be tailored to each dog's minimum threshold for getting a response. If used correctly, training collars do not cause harm to your dog and can, in fact, result in less harm to the dog than if traditional negative reinforcement or punishment was used to stop or force a behavior. Also, if used to prevent a dangerous behavior such as running out into traffic, leaving the yard, or chasing livestock, it can be a life-saving device for a dog that cannot control his natural inclinations and may put himself in harm's way.
A training collar can be set to signal your dog and warn him that a correction is coming, allowing him to cease and correct behavior before receiving stimulation, which is a form of reinforcement, avoidance of a stimulus that is not delivered if the dog attends to commands or corrects their own behavior. This form of training can be very effective and is best used in conjunction with other training methods so that minimal stimulation is required. The stimulation delivered is adjustable, but is similar to a static electricity shock or can even be adjusted to provide a simple vibration to signal your dog and get attention. Training should be conducted at the lowest level of stimulation that elicits a response in your dog to be humane and effective, and to avoid negative side effects such as the development of aggression or anxiety, which can be associated with incorrect use.