Public Latency monitoring

Good Day Sirs, and Ma'am's .

I was wondering if anyone had an easy to setup / maintain monitoring App that can alert when latency thresholds are met. So I use Uptime Robot (love it by the way) to monitor a couple of websites to confirm they are up. It also graphs the load times but I haven't seen a way to alert when those go over a certain threshold.

I've used open nms in the past, and didn't like the upkeep it took(every update seemed like it broke it ). I used PRTG and this would fit the bill, but I'd also like to monitor the PRTG server, so unless I setup a second instance.