Many physical principles have been applied to transform atmospheric pressure fluctuations of 1 sec and longer into electrical signals for the purpose of monitoring infrasonic signals. A survey of some infrasonic sensors is taken, with calibration and testing of several sensors at the UCLA calibration facility. An attempt was made to define the capabilities of each available sensor. Several experiments are described, which include the monitoring of static and dynamic firing of rockets, as well as the monitoring of explosions. The difficulties in interpretation of data are explained in relation to various instruments, taking into account wind effects, ground vibrations (observed by magnetometers), natural pressure fluctuations, and other phenomena producing noise at the frequency range of interest.