This paper presents a platform for context-aware computing that enables applications to follow mobile users as they move around a building. The platform is particularly suitable for richly equipped, networked environments. The only item a user is required to carry is a small sensor tag, which identifies them to the system and locates them accurately in three dimensions. The platform builds a dynamic model of the environment using these location sensors and resource information gathered by telemetry software, and presents it in a form suitable for application programmers. Use of the platform is illustrated through a practical example, which allows a user's current working desktop to follow them as they move around the environment. The platform has five main components: a fine-grained location system, a detailed data model, a persistent distributed object system, resource monitors, and a spatial monitoring service. The location system uses ultrasonic techniques with small units called Bats, which are attached to equipment and carried by personnel. These Bats emit ultrasound pulses that are received by fixed receivers, allowing the system to determine the position of the Bats and, consequently, the objects they are attached to. The system also uses statistical outlier rejection algorithms to eliminate erroneous distance measurements. The platform also includes a data model that describes the essential real-world entities involved in mobile applications. This model is used to represent the environment and its entities in a form suitable for application programmers. The system also includes a resource monitoring system that collects information about the computing environment and allows applications to adjust their behavior to accommodate system capabilities and usage patterns. The paper also describes a Follow-me application called 'Bat Teleporting', which allows a user's desktop to follow them as they move around the environment. The application uses the location system to determine when a user is near a computer and automatically teleports their desktop to that computer. The application is event-driven and uses spatial monitoring to determine when a user is in a specific zone relative to a computer. The platform is scalable and robust, with the ability to handle large numbers of objects and large areas of operation. The system is implemented using a three-tier architecture, with the data model stored in a database and accessed via a proxy server. The system is also able to handle a large number of users and applications, with the ability to scale to support large buildings and environments. The paper concludes that the platform provides a robust, scalable, and usable infrastructure for implementing context-aware systems.This paper presents a platform for context-aware computing that enables applications to follow mobile users as they move around a building. The platform is particularly suitable for richly equipped, networked environments. The only item a user is required to carry is a small sensor tag, which identifies them to the system and locates them accurately in three dimensions. The platform builds a dynamic model of the environment using these location sensors and resource information gathered by telemetry software, and presents it in a form suitable for application programmers. Use of the platform is illustrated through a practical example, which allows a user's current working desktop to follow them as they move around the environment. The platform has five main components: a fine-grained location system, a detailed data model, a persistent distributed object system, resource monitors, and a spatial monitoring service. The location system uses ultrasonic techniques with small units called Bats, which are attached to equipment and carried by personnel. These Bats emit ultrasound pulses that are received by fixed receivers, allowing the system to determine the position of the Bats and, consequently, the objects they are attached to. The system also uses statistical outlier rejection algorithms to eliminate erroneous distance measurements. The platform also includes a data model that describes the essential real-world entities involved in mobile applications. This model is used to represent the environment and its entities in a form suitable for application programmers. The system also includes a resource monitoring system that collects information about the computing environment and allows applications to adjust their behavior to accommodate system capabilities and usage patterns. The paper also describes a Follow-me application called 'Bat Teleporting', which allows a user's desktop to follow them as they move around the environment. The application uses the location system to determine when a user is near a computer and automatically teleports their desktop to that computer. The application is event-driven and uses spatial monitoring to determine when a user is in a specific zone relative to a computer. The platform is scalable and robust, with the ability to handle large numbers of objects and large areas of operation. The system is implemented using a three-tier architecture, with the data model stored in a database and accessed via a proxy server. The system is also able to handle a large number of users and applications, with the ability to scale to support large buildings and environments. The paper concludes that the platform provides a robust, scalable, and usable infrastructure for implementing context-aware systems.