Get Notified on Your iPhone When Your NAS, Plex or Home Server Goes Offline
Short version. There are two mechanisms and they do not overlap. If the server has a public URL (a domain pointed at your Plex, a reverse proxy, a tunnel), Uptime Watch checks it every hour from Cloudflare and pushes when it goes down and when it is back; one URL is free. If it only has a private address, the free PingKit Agent on a Mac notices it missing from three consecutive scans (about 15 minutes by default) and, with Guardian ($2.99/mo), that alert reaches your iPhone. A NAS that emails you about problems cannot email you when it is off.
First, Which Kind of Offline
"My server is down" is three different events with three different fixes. The box itself has stopped: power, a kernel panic, a disk array that will not mount. The box is fine but the internet is down, so you cannot reach it from outside. Or the box is fine and reachable, but the service on it, Plex or Home Assistant or a container, has crashed. A monitor that only checks one of these will tell you the wrong thing at the worst moment, so it is worth knowing which one each route below actually detects.
Route 1: A Public URL, Checked From the Internet
If the server answers on a URL the internet can reach, a domain you have pointed at it, a reverse proxy in front of it, or a tunnel, then Uptime Watch can watch it. Add the URL in PingKit's Monitor tab and PingKit's backend on Cloudflare's network sends an HTTP HEAD request once an hour with a 10-second timeout. Anything other than a 2xx, or no answer, marks it down and sends a push to your iPhone and to the Mac Agent; the next good check sends the recovery. Results are kept for 30 days. One URL is free, permanently; Guardian watches ten.
What this detects: all three kinds of offline at once, because a request from outside fails whether the box, the internet or the service is the thing that broke. What it cannot tell you is which. That is the trade for needing nothing on your network: the check is real, from where your users are, and it runs while your Mac and your phone are off.
What it cannot reach: a private address. 192.168.1.20 does not exist on the internet, and Uptime Watch will not accept it as a target. Plex's own remote access goes through plex.tv and is not a URL you can point a monitor at either; you need a name that resolves to your server directly.
Route 2: A Mac on the LAN, Watching the Box
For everything with only a private address, the answer is a machine on the same network that notices when the box stops answering. The free PingKit Agent for Mac scans the network every five minutes by default and keeps a device list. When a known device has been absent from three consecutive scans, about fifteen minutes at the default interval and adjustable in the Agent's settings, it raises a Device Offline alert on the Mac, and it resolves the alert when the device is seen again. That is free. With Guardian on your iPhone, the same alert arrives on the phone through your private iCloud, wherever you are.
What this detects: the box has gone off the network, which covers power and crashes. It does not detect a service that has died on a box that is still answering ARP, and it does not detect your internet being down, which the Agent reports separately as a connectivity alert. It needs a Mac that stays awake on the same LAN; a Mac mini next to the NAS is the classic setup.
Use Both
A homelab with a Plex behind a domain and a NAS on a private address gets Uptime Watch on the Plex URL and the Agent watching the NAS, and the two alerts together tell you which kind of offline it is: URL down and NAS still on the LAN means the service or the internet; NAS gone from the LAN means the box.
Bringing It Back
If the box supports Wake-on-LAN and the outage was a sleep or a soft shutdown, PingKit's Wake-on-LAN tool sends the magic packet from your iPhone while you are on the same Wi-Fi, and the Mac Agent can send it from the Mac. That does nothing for a kernel panic or a pulled plug, which is why the alert matters: it tells you to go and look.
Why Not Let the NAS Email You
Synology, QNAP and most Linux boxes can send email or push about disk health, temperature and failed logins, and you should turn that on. It covers problems the box can see about itself. It cannot cover the box being off, because a machine that is off sends nothing. The silence is the event, and only something outside the box can notice silence.
Honest Limits
- Uptime Watch is hourly and cannot see private addresses. A crash at 21:05 is reported at the next check, not at 21:05.
- The Agent's offline alert needs a Mac that stays awake on the same network, and it means "not seen on the LAN", not "the service has stopped".
- Neither route restarts anything. They tell you; you fix it.
- Alerts to the iPhone need Guardian. On the Mac itself, everything the Agent does is free.
Frequently Asked Questions
How do I get a notification when my NAS goes offline?
If the NAS has a public URL, add it to PingKit's Uptime Watch and you get a push on your iPhone when the hourly check fails and when it recovers; one URL is free. If it only has a private address, run the free PingKit Agent on a Mac on the same network: it raises a Device Offline alert after the NAS has been missing from three consecutive scans, and Guardian ($2.99 a month) delivers that alert to your iPhone.
Can I get a Plex server down alert on iPhone?
Yes, if the server answers on a domain you control: Uptime Watch checks it hourly from the internet and pushes when it goes down. Plex's remote access through plex.tv is not a monitorable URL, so you need a direct name or a tunnel.
Can Uptime Watch monitor a private IP address like 192.168.1.20?
No. The check runs from Cloudflare's network and can only reach addresses that exist on the internet. For a LAN-only device, use the Mac Agent's Device Offline alert.
How quickly does the Mac Agent notice a device is offline?
After three consecutive scans without it, which is about fifteen minutes at the default five-minute scan interval. Both numbers are adjustable in the Agent's settings.
Does this work without a Mac?
Uptime Watch does: it needs only a public URL and the PingKit app on your iPhone. Watching a LAN-only device needs the Mac Agent, because an iPhone cannot scan the network while its app is closed.
Know before you get home.
Free to download. Guardian is $2.99 a month or $24.99 a year, with a 1-week free trial on both. Cancel anytime. The Mac Agent is free on the Mac App Store.
Download PingKit for iPhone