You can preset a timeout value in your account so when the phone has not updated within this preset value, you receive an email or SMS alert (depending on your alert preference setting). For example, you can get an alert when the phone has not updated in the past 10 minutes.
To set the inactivity alert level for a unit, just login to your AccuTracking account, then click "Account" > "Account Settings", then set "Alert if phone is inactive for X minutes".
Note: The alert preferences need to be set to at least one of the two options "Email" or "SMS" on account setting page: "Account" > "General" > "Account Settings".