The present invention relates to a device for measuring, recording, and acting in response to changes in air pressures encountered through the lumen of a connected needle. The device signals when it has been powered and signals when the device recognizes both pressures and pressure change rates indicative of synovial cavity joint penetration, such as knee joint penetration. Synovial cavity pressures detected and acted upon may either be supra- (positive) or sub-atmospheric (negative). Internal light emitting diodes and a laptop connected display are demonstrated as signaling and communication mechanisms. Methods for delivering medicaments into human and animal intra-articular cavities or joints such as synovial cavities are provided. Furthermore, methods for facilitating the diagnoses of joint effusion also are provided.