This research study is for participants diagnosed with leptomeningeal metastasis disease (LMM), a condition where cancer has spread to the fluid and membranes surround the brain and spinal cord. The purpose of this study is to find out whether a consumer Smartwatch can continuously monitor the participant's health and detect early signs of neurological decline and whether sending an automatic alert to the participant's doctor when a change is detected can help reduce the number of participant hospitalizations.