A mobile personal security device, system and method to accept an activation signal of the system on a mobile device. An input of a periodicity setting is also accepted to indicate one of a series of time periods during which the system expects a security code to be inputted into the device. If the code is inputted into the device during one or each interval, then the interval is reset to expect a further inputting of the code during a subsequent interval. If the code is not received, an alarm signal may be issued.