The equipment used in biofeedback can range from a simple cheap thermometer to a highly expensive EEG machine to monitor your brain activity. The most common biofeedback monitors are for heartbeat, blood pressure, skin temperature, sweat glands, brain activity, and muscle tension - which is by far the most common biofeedback equipment used today.
To monitor muscle tension they use an EMG machine, or better known as an Electromyogram. By using the EMG biofeedback equipment you can learn to control tension and the feeling of it - which means you can make it go away through control - it is mainly used as a relaxation tool to help ease muscles in people who have back aches, head aches, and bruxism.
To monitor your skin temperature using biofeedback equipment you will need is relatively simple - you can feel how warm your skin is, and when your skin cools you know that your body is constricting your blood vessels and is a sing of stress, although there are always special thermometers you can use.
Galvanic skin responses can be monitored with a biofeedback device known as a GSR2, or even common lie detectors can be used, but equipment is always needed - it monitors the sweat glands in your skin and shows you the results which is supposed to train you to be able to control your feelings and responses to stress, and also your sweat responses.
Monitoring the brain is done through electroencephalography, or EEG, and this biofeedback equipment does not come cheap. The EEG monitors the activity of brain waves when linked to different areas and mental states, able to see how you are when you are awake, relaxing, calm, or sleeping. This is the least common form of biofeedback as the biofeedback equipment is the most costly and is very technical, requiring much training to use.