Pingdom is a service that tracks the availability (e.g. uptime & downtime) as well as the performance of websites. It's been around for ages and is a tried-and-true method for being alerted when there's an outage. They also have a feature called “Real User Monitoring” that uses a little bit of javascript to determine how fast your pages are loading for real end-users. Real-user-monitoring is essential for catching brown-outs where the site might be “up” but degraded. The company is based in Sweden, but they monitor your websites from multiple locations around the world so that they can distinguish between outages from localized network routing problems. They will also produce a `traceroute` from a location that has connectivity problems so you can help identify where in the network path traffic is affected.