Review on Milton M Style Button Safety Coupler S-99706, Push Button To Stop Airflow And Release Plug, Prevent Accidental Disconnects, 1/4" Male NPT by Scott Hall

These are a must have when using an air compressor. The way these work is when you want to disconnect from the air line you depress the button once and it lets off air pressure, the second time the button is pressed it releases and there is minimal pressure if any. This is a much safer way to disconnect from an air supply. These compared to others on the market are heavy duty and solid, very well made. The units from Home Depot and Harbor Freight are much lighter and my guess less heavy duty. I find these to be the same cost as the inferior units.