During a typical biofeedback session, small electrodes are attached to your skin with adhesive, or alternatively the practitioner may use finger sensors. Signals from these sensors are then sent to a monitor which displays a sound, flash of light, or image that represents your heart and breathing rate, blood pressure, skin temperature, sweating, or muscle activity.
These functions change drastically even under moderate stress. Your heart rate increases, muscles tighten, blood pressure rises, you start to sweat, and your breathing quickens. The monitor displays these changes in real time as you experience them, and then you are able to get immediate feedback as you try to stop them. Typically sessions are done in a therapist's office, but there are computer programs that connect the biofeedback sensor to your own computer at home.
Recently, biofeedback has enjoyed much popularity with other modalities such as NAET for allergy elimination because even the smallest increment of stress can be measured as an indication of a potential allergen to the immune system.