Refer to the following steps: 

1. Tap the Notification widget to get the Notification Settings page:

2. The Notification widget settings provide the following options:
   • NOTIFY WHEN HARDWARE GOES OFFLINE: The user will get a push notification to their smartphone or tablet if the Raspberry Pi goes offline. Under NOTIFY WHEN HARDWARE GOES OFFLINE, simply slide the button to the ON position to enable this feature.
   • OFFLINE IGNORE PERIOD: If you enable this option, you can further define how long the Raspberry Pi can be offline before sending a notification:

3. Under OFFLINE IGNORE PERIOD, tap the drop-down list and choose one of the items. Instant means there is no ignore period, so the Raspberry Pi will immediately send a notification to the user if it goes offline. You can choose the time, between 1 second and 24 hours:

• PRIORITY: The second option, PRIORITY, could be either NORMAL or high. HIGH priority gives a greater chance that your message will be delivered without any delays.
• RINGTONE: The last option allows you to select a ringtone for the notification. The default ringtone is BONGO! You can select a ringtone from Media Storage or Themes from your smartphone or tablet:

Blynk allows you to send one notification every 15 seconds.