How it works
Checks run from Cloudflare servers every 5 minutes. If a target does not answer we retry a minute later and only alert after two failures in a row, so a single network blip does not wake you up. When it answers again you get a message with the downtime.
Why SIP has its own check
An open port 5060 does not mean the PBX is alive: Asterisk can hang while the port stays open. We send a real SIP OPTIONS and wait for an answer, the same way carriers qualify trunks.
Limits
Up to 5 watches per chat, a 5-minute interval, checked from one location (Europe). Private addresses and port 25 cannot be checked. If a target never answered since it was added, we do not send down alerts, only when it comes up.
One-off checks: is it down, port check, SIP check. All bot commands: Telegram bot.