Create a cost effective power outage detector for SDWAN

As cheap as Slaptjips

In South Africa we have been suffering from plenty of power outages caused by loadshedding. This lead me to consider what is the most cost effective method to detect a power outage.

This little puppy which is available here is known as an Internet Power Unit and powers a fibre ONT as well as a SDWAN node which both operate at 12V. It has 2 x batteries which easily keep the networking kit up for over 4 hours. Thus during a power outage the network links remain powered up.

The best method to provide a failover link for SDWAN is to use an LTE modem. This LTE modem can easily be powered via the USB port of the SDWAN node. The modem that is typically used is this one from Mikrotik:

This is known as a Mikrotik LTAP which is available here. When this is used with a SDWAN node it is connected via an Ethernet cable and the on-board WiFi is disabled. I was pondering a cost effective power outage detector and then this idea hit me…

The first thing to do is enable the on-board WiFi on the LTAP and assign a non-routable subnet on an SSID that is used exclusively for maintenance (it has no internet access). This SSID is used to install WiFI repeaters like this type available here. These are as cheap as chips and are less than a Mandela Leopard each. These WiFi repeaters are installed using power that does not have a path through a UPS.

The trick is to now ping the Wifi repeater from the LTAP using Netwatch. Should that ping test fail then the LTAP sends an SMS to you that a power outage has occurred. Alternatively, you can send an email if you are using a rain SIM.

Anyone who can think of a cheaper solution, please leave a comment below!