Probably the only downside of the mathematical method may be, sensitivity to extreme lighting conditions or the need for an external object (other than your body), to trigger the alarm. To address this drawback, we can also use gesture recognition models optimized by OpenVINOto recognize sign languages and trigger alerts. You can also train a custom gesture of your own, as explained here.
However, some layers of such OpenVINO models are not supported by MYRIAD device as given in the table here. Hence, this module needs to be hosted on a remote server as an API.