Abstract: A wearable computing device includes a plurality of biometric sensors configured to determine biometric parameters of a wearer of the wearable computing device, and a plurality of modules configured to determine activity parameters of the wearer. A first module directly subscribes to receive a first biometric parameter from a first biometric sensor. A subscription of the first module to the first biometric sensor specifies activation of the first biometric sensor to provide the first biometric parameter to the first module. The first module derives a first activity parameter from the first biometric parameter. A second module indirectly subscribes to the first biometric sensor by directly subscribing to receive the first activity parameter from the first module. A subscription of the second module to the first module specifies activation of the first module to provide the first activity parameter to the second module.