Opt in to the Scanner Appliance Heartbeat Check notification and you'll get an email when we discover your appliance is offline after some number of heartbeat checks (1-5). You can configure this in the appliance settings (just go to Scans > Appliances and edit the appliance).
We attempt to make a connection with each appliance every 4 hours to see if it's up and running. This heartbeat check lets you know whether the appliance is ready to perform scans and is able to get the most recent software updates.
The email notifications are sent at the following GMT schedule. This schedule is fixed and does not change based on the missed heartbeat.
00:00
04:00
08:00
12:00
16:00
20:00
00:00
The first notification email time varies depending on when the Qualys system receives the missed heartbeat. Subsequent notification emails are then sent every 4 hours thereafter.
Here are the first notification email examples for the missed heartbeat (1):
If the Scanner becomes disconnected at 02:00 AM GMT, then Qualys system will wait 4 hours before sending the first email notification. In this case, the system will wait until 06:00 AM GMT. Since there is a pre-set schedule for sending notification emails, the first notification will be sent at 08:00 AM GMT. It means the Qualys system will send the first notification 6 hours after the heartbeat was missed. Subsequently, the second notification email will be sent 4 hours after the first one, and the process will continue.
While sending notification emails, the Qualys system considers only the hours part of the time. For example, If the scanner disconnects at 12.57 PM GMT, the system will consider the time 12 PM GMT and send the notification email at 16 PM GMT.
1) Go to Scans > Appliances. Edit your appliance (hover over an appliance and select Edit from the menu). Under General Information, select the Notification option and the number of missed heartbeat checks before we'll send you an email.
2) Select User Profile below your user name (in the top right corner). Go to Options and select the "Scanner Appliance heartbeat check" notification option.
You can tell whether your appliance is online by going to the scanner appliances list (Scans > Appliances). You'll see 
(Connected) next to your appliance when it is ready to process scans. Select the appliance and check the preview pane to see the number of heartbeat checks missed if any. If there's missed checks, it's possible the appliance has come back up since the time of the last check. As long as you see the appliance is ready for scanning and there's no reason for concern.
If an email address is associated with multiple user accounts and the "Scanner offline" notification checkbox is checked, the notification will be sent to the same email address for each individual user account. This means that the scanner offline email will be sent multiple times to the same recipient email address in this case.