Since 15:23 UTC every monitor on every account can be checked every 10 seconds, free or paid, verified or not: HTTP(S), TLS, ping, TCP, SMTP and DNS alike. Before, anything under 30 seconds needed a verified domain or a credit purchase, 10 seconds needed both, and ping was limited to once a minute. A faster interval simply uses more credits, at one credit per round as always; the free 650,000 credits a month cover two monitors at 10 seconds or fifteen at one minute.
At the same time TCP, SMTP and DNS checks no longer need a verified domain on the common ports: 22, 25, 53, 110, 143, 465, 587, 993, 995, 3306 and 5432, on hostnames and IP addresses alike. A hosting provider can now monitor its nameservers, mail servers and SSH the minute it signs up. Verification is still needed for any other port, and for HTTP requests with another method, a body, Basic auth or secret headers. When a monitor needs it, the form now names the domain and has a Verify button that brings you back to the form with what you typed.
Nothing changes in how a site is protected from us: one host is checked at most 12 rounds a minute across all accounts, and anyone can ask [email protected] to stop all checks of their address. The Terms and the Acceptable Use Policy say the same since 15:21 UTC; Intervals and credits and Domain verification have the details.
Since 15:36 UTC an import from updown.io, UptimeRobot or a file, and Quick add, keep a 10-second interval instead of turning it into 15 seconds.
When you connect an Enhance panel you now also choose how often its sites are checked, with the monthly cost for your number of sites shown next to each choice before anything is imported, and you can change it for all of them later on the connection's page.