The present invention provides an automatic blood pressure monitor for measuring the arterial blood pressure at a location on a patient. The automatic monitor of the invention does not require an external pump of any type. The invention uses a propellant supply chamber containing a predetermined quantity of propellant in order to inflate a pressure occluding bladder, thus allowing the measurement to be made. All of the elements comprising the monitor are attached to or are an integral part of a strap, which supports the monitor at the desired location on the patient. The monitor of the invention is inexpensive and simple to operate and can be used by non-professional persons in non-clinical or non-laboratory environments.