A system for critical time-based opioid monitoring system includes a physiological monitoring system having a sensor and a system processing board, a computing device configured to receive the parameters, an indication of normal conditions of a user under the circumstances at the time, such as, for example, a body transfer function or user physiological parameter model, to compare the monitored parameters to the normal conditions, and sending a notification when the monitored parameters deviate from the normal condition of a user. A system to monitor for an opioid event includes a physiological monitoring system comprising a sensor configured to monitor physiological parameters and a signal processing board, a computing device to detect an opioid overdose, and a device to stimulate a response when the computing device detects an opioid overdose event is occurring.