This paper describes new methods to quantify safety of sense and avoid (SAA) functions for Unmanned Aircraft Systems (UAS) by evaluating integrity and continuity risks. These methods can set sensor requirements. The closest point of approach (CPA) distance and time to CPA, tau, are used to measure the hazards associated with the intruder aircraft. This paper presents a method to determine hazard state estimates and estimate error. These variances are used to establish (1) the integrity risk of the SAA system not detecting imminent loss of self-separation and (2) the probability of false alert, the continuity risk. A preliminary analysis assumes a constant relative velocity model with normal, independent and stationary measurement errors. A sensitivity analysis evaluates the impact on integrity and continuity of sensor noise, range and sample interval. This research can set potential SAA sensor requirements for UAS integration into the National Airspace System.