Motivation. As technological developments in the workplace accelerate, workplaces are connecting to a variety of sensors, actuators, and dedicated networks in the Internet of Things (IoT). Sensor data can be collected on aspects of workplace performance and occupants’ behaviors. While the performance of the workplace is evaluated, the validation by facility managers is under-development and dominated by perceptual self-report measurements. In Post Occupancy Evaluation (POE) the main instrument used by facility managers is surveys. Due to the properties of the instruments, surveys and other self-report measurements raise concern for the effectiveness of verifications to maintain and improve the performance of the workplace environment. With new ways of working, Activity-Based Working (ABW) is a promising workstyle focused on people, place, and technology, but several performance issues have been identified. Limited studies focus on the application of sensor data, and IoT is only recently recognized to make a significant impact on the validation of the workplace performance by facility managers. Research aim and goal. The main research aim is to explore the application of sensor data for the validation of the ABW performance by facility managers. The research goal is to identify the opportunities and limitations of the current sensor data in an IoT from a Facility Management (FM) perspective. Research method. The exploration of the sensor data is conducted utilizing both research and design in a case study. The case study is a prominent smart building located at Schiphol that has embraced the concept of ABW. In the case study, the available sensor data is collected and explored for opportunities and limitations. Components of an interface are designed from a FM perspective to explore the sensor data structurally in an ABW environment. The exploration of the data is conducted using hypotheses. Three hypotheses are formulated based on performance issues in ABW from literature, and further specified based on the case study. Key findings and conclusion. The exploration of the sensor data illustrated that the role and decision-making process of a facility manager can drastically change within the ABW environment of smart buildings. The facility manager can validate the workplace performance with goals set for each activity. Facility managers can shift from a complaint-driven reactive attitude to a proactive data-driven analytic of the workplace performance. With the sensor data, the facility manager can additionally rely on continuous quantitative and objective data of the workplace performance. The use of both subjective inputs from occupants’ perception in combination with objective sensor data can improve the reliability of the data for more effective verifications in the ABW environment. Nevertheless, the current state of smart buildings is not up to expectations. The sensor data is the critical input in an IoT and lacks on many fronts. Researchers and practitioners are encouraged to align the data of the sensors with KPIs from a facility management perspective by (re)considering the functionality of the sensors. To benchmark the sensor data with aspects of employee satisfaction, productivity, and well-being, a consensus is required amongst organizations for the application of sensors with similar output values.