1. A multi-device alert notification system comprising: a trigger device comprising a trigger element and a low energy wireless transmitter for broadcasting an alert message in unlicensed spectrum directly to mobile user devices when the trigger element is activated, the alert message comprising a unique trigger device identifier; a remote server system storing information that identifies the trigger device, the remote server being configured to: receive, through a network, an alert notification message from each of a plurality of mobile user devices, each alert notification message indicating that the mobile user device has received the alert message directly from the trigger device through the unlicensed spectrum and including the unique trigger device identifier and a unique user identifier associated with the mobile user device; receive, through the network, an alert acceptance request message from one of the mobile user devices that includes the unique trigger device identifier and the unique user identifier associated with the mobile user device; and send notification messages to at least the mobile user devices that did not send the alert acceptance request message, the notification messages indicating that the alert message from the trigger device has been accepted by one of the plurality of mobile user devices.