Recently, WISP tags, one latest extension of RFID tags, have been used to identify indoor activity recognition, vital signs, sleep quality, and in other health status monitoring systems. It has also been used in many assisted environments or elderly care systems. However, these systems challenge current state-of-the-art techniques for accuracy, reliability, and security. This paper studies the problem of monitoring a large set of WISP tags and identifying the missing ones. The missing WISP tag data may introduce errors in the health status monitoring system and may result in reduced system security and accuracy. Therefore, in order to maintain system accuracy, a monitoring protocol needs to be executed frequently and it should be made efficient in terms of execution time. In this paper, based on probabilistic methods, we propose two tag monitoring protocols, Monitor and Collect (MonAC), for WISP based environments. The goal of these protocols is to improve the accuracy of health status monitoring environments or assisted care environments by detecting missing tags and reporting back only the sensor data of the existing tags.