Uptime/Downtime Monitoring Services
Website downtime frustrates visitors and hurts your search engine rankings. It can indicate deeper trouble for web developers, especially if it occurs too frequently. It's best to know when your site is down as soon as possible.
Many of these services also offer premium plans. Paid plans may offer monitoring of more sites, more frequent checking intervals, more types of alerts, and additional services. It is worth considering paid plans if you depend on your website for leads, sales, customer support or any other vital functions.
Some of these require you to create a free account and login before using.
Pingdom
https://www.pingdom.com/
Free uptime monitoring service plus other useful tools such as speed testing, DNS health checks, pings and traceroutes.
Premium plans start at $6.96 per month. 10 checks plus 20 sms alerts per month. Free plan monitors one website/server and includes Real User Monitoring.
Uptime Robot
http://uptimerobot.com/
Free. No paid plans. Up to 50 checks (websites or servers), at 5 minute intervals.
Monitor.us
http://www.monitor.us/en/website-monitoring
Free. No gimmicks, no contracts. Quick setup. Website and network monitoring, page load monitoring, server monitoring and mobile monitoring.
Status Cake
https://www.statuscake.com/
Choose where your website’s uptime is monitored from and frequency. 5 minute check intervals. Browser testing feature.
Host Tracker
http://www.host-tracker.com/
free uptime monitoring plan. 2 URLs with 30 minutes monitoring interval each. Premium plans from $3.25 per month for 5 URLs with 10 minutes checking intervals.
Basic State
http://basicstate.com/
Checks network outages, server outages, server overload, dns configuration problems. 15 minutes check intervals. Email alerts. Daily uptime reports include 14-day history.
MonTools
http://montools.com/
Simple interface. Many features. Check website or server at your choice of regular intervals. Email alerts, sms, twitter. Even the free plan can have website monitoring, https monitoring, FTP monitoring, Apache monitoring, MySQL monitoring, IMAP, POP3 and SMTP monitoring plus DNS and Ping monitoring.
Uptime Spy
http://www.uptimespy.com/
Free plan gives 1 check or 1 website to monitor. Premimum plan allows monitoring up to 30 websites. Uptime Reports, Multiple Location Checks, Public and Email Reports.
Site 24×7
http://www.site24x7.com/
Free basic monitoring of 5 websites at 10 minute intervals.
Montastic
http://www.montastic.com/
Free monitoring every 30 minutes
Free Site Status
http://www.freesitestatus.com/en/compare.php
Free monitoring of websites and servers from different locations every 60 minutes.
Site Uptime
http://www.siteuptime.com/
Free for 1 monitor, 30 to 60 minute invervals, public stat
Internetseer
http://www.internetseer.com/
Featuring false alarm protection. Free plan has 60 minutes monitoring intervals.
LiveWatch
http://www.livewatch.de/en/
Free for 1 monitor, 10 minute intervals. 1 sms alert is available for per month.
Uptime Dog
http://www.uptimedog.com/
Free website monitoring at 2 minute intervals, email notifications.
Service Uptime
http://www.serviceuptime.com/
Monitor one site or server every 30 minutes
100 Pulse
http://100pulse.com/pricing.jsp
Monitor 2 sites at 15 minute intervals
Binary Canary
http://binarycanary.com/
Free monitoring of up to 5 http/https pages at 15 minute intervals
New Relic
http://newrelic.com/server-monitoring
Also monitors performance of web apps, mobile apps, servers, database and caching. Free server monitoring with alerts for server health issues, CPU utilization, memory utilization, disk I/O utilization, and disk capacity. Basic feature plan with 24 hours data retention, with no advanced priority support.
Anturis
https://anturis.com/pricing/
Free website monitoring for up to 5 sites with 1 minute polling intervals, unlimited email alerts.