To use /devices/[serial]/clients, you first need the serial number of the device you want to check.  You can get the serial number from another API (network or inventory) or from the Meraki Dashboard UI.   When you make the clients API call, you must include a parameter 'timespan'.  This parameter tells the API how far back you want to look when listing clients (in seconds).  For your use case, you might call the API with a timespan of 1 hour (3600 seconds) and again with a timespan of 1 day (86400 seconds).  For any devices that appear in the 1-day query but not in the 1 hour query, you would revoke the splash authorization through the API call I already mentioned.   With the Scanning API, you would listen for data from Meraki, keep a list of devices and when you last saw them, and revoke authorization when a device disappears for a predefined period of time.   ... View more