What are some alternatives?
UptimeRobot - Free Website Uptime Monitoring
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
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.
updown.io - updown.io is a HTTP(S)/TCP/ICMP monitoring service which checks periodically the URL you want and reports back any anomaly.
SiteUptime - Siteuptime provides website monitoring services. Receive instant email and SMS alerts when your website becomes unavailable. View detailed uptime statistics and performance reports for your website monitors.