Overview: In the concealed information polygraph test, suspects are well aware that they are being interrogated and that their physiological responses are being monitored. Such awareness may result in countermeasure attempts by guilty suspects while trying to escape detection. To combat countermeasures, it is possible to remove the standard polygraph sensors and replace them with covert respiration measures. The rationale is that guilty suspects would shift attention from their physiological reaction to the more familiar verbal and facial expressions. The present chapter introduces covert respiration measures and describes how they can be used to reduce countermeasures. Another question is whether covert respiration measures may serve to reduce excitement of overexcited examinees. The issue is further discussed. Attention is also given to early attempts to apply covert voice analysis and to more recent attempts to measure thermal imaging from a distance. Finally, ethical and moral considerations involved in using covert measures are discussed.