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.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Downtime Bot for Telegram - Get alerts when your site gives errors via a Telegram Bot 🤖
Better Uptime - We call you when your website goes down
TaskCall - TaskCall is an incident response and management service that helps organizations digitize their operations and reduce downtime costs to the minimum by mobilizing their response effort and streamlining stakeholder communication.