What are some alternatives?
When comparing PerfectPage and updown.io, you can also consider the following products
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
UptimeRobot - Free Website Uptime Monitoring
StatusCake - StatusCake | Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Apex Ping - Uptime & performance monitoring for websites and APIs.
RapidSpike - RapidSpike is an uptime and performance monitoring service for websites and web applications.
Downtime Monkey - Downtime Monkey: website downtime alerts & uptime monitoring worldwide.