Pi.Alert: Know When Something Changes on Your Network

You probably have a rough idea of what's on your network, but do you actually know the moment a new device shows up or a familiar one drops off? Pi.Alert is an open-source tool that watches your Wi-Fi and LAN, discovers devices, tracks their availability, and tells you when something changes. It runs on a Raspberry Pi (or another Debian-based system) and gives you a web interface to manage the whole thing.

What It Does

Pi.Alert discovers devices connected to your Wi-Fi or LAN and tracks whether they're online. It can notify you when an unknown device appears or a known one goes offline. Beyond basic device discovery, it monitors devices outside your local subnet using ICMP, detects unwanted or foreign DHCP servers, and keeps an eye on internal and external web services by checking HTTP status, response time, and SSL certificate information. You'll get an alert when a monitored service becomes unavailable or when its status or certificate changes.

The backend is typically started by cron every five minutes. It runs whatever scans and imports you've configured, stores the results, and sends notifications when relevant changes are detected. Notifications can go through the frontend, email, Pushsafer, Pushover, ntfy, or Telegram. The web interface lets you review current and historical device data, add owners and locations, organize network relationships, configure settings, and view events and reports. There's also an API you can hook into things like Home Assistant or Homepage.

Why It's Cool

• It plays nicely with what you already run. Pi.Alert can pull device information from a lot of sources: arp-scan for local discovery, Pi-hole 5 and 6, FRITZ!Box, MikroTik, UniFi, OpenWrt, AsusWRT, pfSense, OPNsense, and AdGuard Home. If you've already got a router or DNS setup doing useful work, you don't have to throw it away to get network visibility.

• The notification options are broad without being annoying. Frontend, email, Pushsafer, Pushover, ntfy, and Telegram cover most of the reasonable ways you'd want to hear about a new device on your network. You pick what fits your workflow instead of being locked into one channel.

• It goes beyond "is it pingable." Web service monitoring with SSL certificate checks is a genuinely useful addition. Certificates expiring quietly are one of those problems that bite you at the worst possible time, and having them watched by the same tool that tracks your devices is convenient.

• The satellite project handles multiple network segments. If you need visibility into another network segment, Pi.Alert-Satellite can scan independently and send results back to your main instance. That's a clean way to extend coverage without overcomplicating the core install.

• The interface is genuinely international. English, German, Spanish, French, Italian, Polish, Danish, Dutch, Czech, Finnish, Swedish, Norwegian, Lithuanian, Ukrainian, and Russian. That's a lot of languages for a self-hosted network tool, and it suggests a real user base beyond the original author.

• Small touches that matter. Login protection is enabled during installation with a randomly generated password (changeable later via pialert-cli), and skin-specific favicons and home-screen icons are included—with direct links from the repo when iOS refuses to load icons from an HTTP or self-signed HTTPS install. That last detail is the kind of thing you only think of after dealing with real users.

How to Try It

Pi.Alert targets Debian-based systems using apt. It was originally designed for the Raspberry Pi, but it runs on DietPi, Ubuntu Server, and other Debian-based distributions—check the distribution notes before you start.

Run the installer as root:

sudo bash -c "$(wget -qLO - https://github.com/leiweibau/Pi.Alert/raw/main/install/pialert_install.sh)"

Once installation completes, continue with the setup steps in the repository. You'll want to configure your scan sources and notification channels through the web interface. The docs folder has setup guides for email and Telegram notifications, plus notes on API usage if you're wiring it into Home Assistant or Homepage.

The project lives at github.com/leiweibau/pi.alert, and the companion satellite scanner is at github.com/leiweibau/Pi.Alert-Satellite.

Final Thoughts

Pi.Alert is a solid fit for homelab folks and small-network admins who want passive awareness of what's connecting and what's falling off—without standing up a full monitoring stack. The breadth of supported scan sources means it'll likely slot into an environment you already have rather than demanding you rebuild it. If you've got a Raspberry Pi sitting around and you've ever wondered "wait, what was that device?", this is a reasonable place to start.

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