Abstract: Several techniques are provided for aiding in the discrimination of detected biological signals indicative of blood pressure from detected signals not indicative of blood pressure (e.g., noise). A threshold, based predominantly on a level of noise, is developed and used in the discrimination. A second threshold, based predominantly on levels of previously detected biological signals, is developed and additionally used to help discriminate the biological signals from noise. The biological signals are detected during a selected portion of a cardiac cycle, and additional signals detected outside of the selected portion of the cycle are applied to the detected signals. Another threshold may be developed based predominantly on a level of signals sensed by a transducer positioned to preferentially sense noise; the transducer is positioned so that the noise that it detects is related to noise that is detected during the detection of the biological signals.