Does anybody have experience with a device/software that pings you when a gateway goes down?

So, we have 15 locations and one thing I was thinking about was a device or software that will possibly email me when it's unable to ping our routers. For instance if 10.0.23.254 which is our default gateway goes down, it would send an email to a specified address alerting of such. I'm thinking it would have to be on a far side of the network because obviously if a location goes down they cant tell us themselves. Any ideas?

Edit: just realized that the title is worded poorly. Damn proof reading.