What are some alternatives?
When comparing updown.io and UptimeRobot, 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.
StatusCake - StatusCake | Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Apex Ping - Uptime & performance monitoring for websites and APIs.
Site24x7 - Site24x7 offers both free & paid website monitoring services. Monitor websites remotely and receive instant email/sms alerts if your website becomes unavailable. View uptime & performance graphs of your website monitors.
RapidSpike - RapidSpike is an uptime and performance monitoring service for websites and web applications.
Downtime Monkey - Downtime Monkey: website downtime alerts & uptime monitoring worldwide.