A method (200, 700) comprising: generating a signal from an energy receiver of a wearable photoplethysmography device, the signal generated by the energy receiver, at least in part, being based upon at least a portion of energy that was initially projected by an energy transmitter of the wearable photoplethysmography device operating to measure medical signs of a user; selecting a subset of wave features of a plurality of wave features of the signal; determining wave metric calculations of a set of wave metric calculations for the subset of wave features; classifying the signal by applying a validity classifier to the wave metric calculations of the set of wave metric calculations to generate a plurality of validity scores for the signal, the validity classifier generated based on the set of wave metric calculations and used to determine if the wearable photoplethysmography device is correctly positioned on the user; applying temporal smoothing to the plurality of validity scores for the signal to generate a smoothed validity score; comparing the smoothed validity score to a validity threshold to determine if the wearable photoplethysmography device is correctly positioned in operating to measure the medical signs of the user, wherein the validity threshold is pre-set or selected based on one or a combination of the wearable photoplethysmography device type, medical signs being measured by the wearable phtotplethysmography device, characteristics of the user of the wearable photoplethysmography device; controlling operation of the wearable photoplethysmography device based on whether it is determined the wearable photoplethysmography device is correctly positioned in operating to measure the medical signs of the user based on a comparison of the smoothed validity score to the validity threshold, wherein controlling operation of the wearable photoplethysmography device includes deactivating the wearable photoplethysmography device, operation in a reduced capacity, deactivating one or more components of the wearable photoplethysmography device, or operating the wearable photoplethysmography device to consume a reduced amount of power. generating a signal from an energy receiver of a wearable photoplethysmography device, the signal generated by the energy receiver, at least in part, being based upon at least a portion of energy that was initially projected by an energy transmitter of the wearable photoplethysmography device operating to measure medical signs of a user; selecting a subset of wave features of a plurality of wave features of the signal; determining wave metric calculations of a set of wave metric calculations for the subset of wave features; classifying the signal by applying a validity classifier to the wave metric calculations of the set of wave metric calculations to generate a plurality of validity scores for the signal, the validity classifier generated based on the set of wave metric calculations and used to determine if the wearable photoplethysmography device is correctly positioned on the user; applying temporal smoothing to the plurality of validity scores for the signal to generate a smoothed validity score; comparing the smoothed validity score to a validity threshold to determine if the wearable photoplethysmography device is correctly positioned in operating to measure the medical signs of the user, wherein the validity threshold is pre-set or selected based on one or a combination of the wearable photoplethysmography device type, medical signs being measured by the wearable phtotplethysmography device, characteristics of the user of the wearable photoplethysmography device; controlling operation of the wearable photoplethysmography device based on whether it is determined the wearable photoplethysmography device is correctly positioned in operating to measure the medical signs of the user based on a comparison of the smoothed validity score to the validity threshold, wherein controlling operation of the wearable photoplethysmography device includes deactivating the wearable photoplethysmography device, operation in a reduced capacity, deactivating one or more components of the wearable photoplethysmography device, or operating the wearable photoplethysmography device to consume a reduced amount of power.