Guide · Alarms after the NBN switch
Alarm stopped working after the NBN? Here's the fix.
Here's the short version. When the NBN came in, the old copper phone line went away, and every alarm that quietly dialled out over it lost its voice: back to base security panels, medical pendants, lift phones, fire panels. Most failed silently, and nobody noticed. The usual fix is a small 4G dialler: cheap, fitted in about an hour, and your existing alarm keeps working. Here's how to test yours today and pick the right fix.
Last updated 2 July 2026 · by Alien IT Solutions
The failure nobody notices
An alarm that can't report is a very convincing prop. The keypad lights up, the panel arms, the siren screams when you trip it. The dialler is the one part you never touch, so when the NBN switch took the phone line out from under it, there was no error beep and no flashing light. It just stopped talking.
Plenty of alarms have sat like that for years, and the owners found out on the worst possible day. If your alarm went in before the NBN did, and nobody touched it during the switch, assume it isn't reporting until you prove otherwise.
Why the NBN broke your alarm
The old copper line was a simple analogue circuit, and your dialler was built for it: pick up the line, hear dial tone, call the monitoring centre and sing the report down the wire in precise analogue tones. Crude, and close to bulletproof.
The phone port on an NBN router is a different animal: an internet phone service that imitates a line closely enough for human ears. Machines are fussier. The compression that squeezes your voice down the pipe mangles alarm tones, so some signals arrive, some vanish, and which you get changes day to day.
And the copper line carried its own power from the exchange, so the alarm could phone for help while the whole house was dark. An NBN router dies the instant the power does.
So even if your installer plugged the alarm into the router's phone port during the switch, you didn't get a fix. You got a maybe.
Check if yours is affected, today
Don't guess. Fifteen minutes settles it for good.
- Work out how it reports. A back to base contract or a medical alarm means a monitoring centre is supposed to hear from your system. Some older setups just dial your own mobile instead.
- Trigger a test signal. Most panels have a test function. No manual? Ring the monitoring centre, say you're testing, then trip the alarm. If it self-dials your mobile, trip it and see if your phone rings.
- Ask the monitoring centre one question: when did you last receive a signal from this system? If the answer lands anywhere near the date your NBN was connected, you have your answer.
The silence is the scary part. Nothing at your end looks wrong, so the check has to happen at their end. A centre that hasn't heard from your alarm in three years has been guarding an empty phone line.
The fix ladder, honestly
Start at step one and only move down with a real reason.
Fit a 4G dialler retrofit
A small module with a SIM that wires into your existing panel and presents itself as a phone line. The panel dials as it always did; the module carries the signal over the mobile network instead. Cheap, keeps the alarm you already own, fitted by a technician in about an hour. For most people this is the whole fix.
Or the provider's own 4G module
On a back to base contract, the monitoring company will usually push their own 4G comms unit. It costs more than a generic dialler, but the path is supervised end to end: if the module stops checking in, they know within hours instead of never. That supervision is worth paying for.
Add IP monitoring as a second path
IP modules report over your internet connection. Fast and cheap to run, but they share a fate with your router: a blackout, an NBN outage or an unplugged cable and they're mute. Good as a second path alongside 4G, weak as the only one.
Modernise the panel when it's earned it
If the panel is decades old, parts are gone, or the retrofit quote creeps toward the cost of a new system, replace it; current panels have 4G and IP built in. But a working panel with dead comms needs comms, not replacement. Don't let anyone start you on this rung.
The SIM: spend little, but never let it lapse
The dialler needs a SIM, and this is where people overspend or get burnt. An alarm sends a handful of tiny signals a month, so the lowest-cost prepaid or IoT SIM you can find does the job. Don't put a full phone plan in it.
Two traps. First, expiry: prepaid SIMs lapse if you don't recharge, and a lapsed SIM is a silent alarm again, the exact fault you just paid to fix. Put the recharge date in your calendar, recurring, and treat it like smoke alarm batteries. Second, the network: 2G and 3G are switched off, so an old GSM dialler is landfill. Whatever you fit must be 4G.
The blackout test
No power means no router, no phone port and no internet, immediately. And a blackout is exactly when break-ins and medical emergencies get more likely, not less.
The rule: every link in the chain needs its own battery. Your panel has one, a decent 4G dialler has one, the mobile towers have theirs. Chain those together and the alarm keeps reporting mid-blackout while the router sits dead on the shelf. If you're rural or lose power every storm season, this alone decides it in favour of 4G.
Medical alarms: extra care, no shortcuts
Everything above applies double when the alarm is a pendant around someone's neck. The NBN rollout kept a register of medical alarm users so nobody was cut over blind. The rollout is finished, but the principle stands: your alarm provider and the monitoring centre both need to know the alarm now sits on an NBN connection, and it's on them to confirm the equipment suits it.
Then prove it: press the pendant's test button and confirm a person at the monitoring centre actually received it over the new connection. Ask what happens in a blackout. If the alarm belongs to a parent who lives alone, do this today. This is not a category to be optimistic in.
Questions people ask
Why did my alarm stop working after the NBN?
Because the copper phone line it dialled out on no longer exists. The NBN replaced it, and the phone port on an NBN router is an internet phone service, not a real line. Alarm diallers talk in precise analogue tones that internet phone services often mangle, so the panel keeps trying to report and nothing arrives. The failure is silent: the siren and sensors still work, the reporting does not.
Can a back to base alarm work on the NBN phone port?
Sometimes, and that is the problem. The tones get through on some connections and not others, and a setup that works today can fail after a firmware update or a network change. The port also goes dead the moment the power does. Treat the router phone port as unfit for alarm reporting and put the alarm on a 4G path instead.
What is a 4G alarm dialler?
A small module with a SIM card that connects to your existing alarm panel and presents itself as a phone line. The panel dials exactly as it always did, and the module carries the signal over the mobile network instead of the dead copper. It keeps your existing alarm, an alarm technician can fit one in about an hour, and it is the cheapest reliable fix.
Is my medical alarm NBN compatible?
Ask the provider directly, and tell the monitoring centre you are on the NBN; both need to know. Then prove it: press the test button and confirm the monitoring centre actually received the call over the new connection. Ask what happens in a blackout too, because the NBN router will be off and the alarm needs its own battery-backed path, usually 4G.
What SIM should go in an alarm dialler?
A cheap one. The dialler sends a handful of tiny signals a month, so the lowest-cost prepaid or IoT SIM you can get does the job. Two rules: the module itself must be 4G, because the 2G and 3G networks are switched off, and the SIM's recharge or expiry date goes in your calendar as a recurring reminder. A lapsed SIM puts you straight back to a silent alarm.
Will my alarm still report during a blackout?
Only if every link in the chain has a battery. Your panel has one, a decent 4G dialler has one, and the mobile towers have theirs. An NBN router does not; it goes dark the second the power fails, which is exactly when you need the alarm most. That is the strongest reason to report over 4G rather than over your internet connection.
Still paying for the line the alarm used to need?
Plenty of bills still carry a landline that only ever existed for the alarm. Once the alarm reports over 4G, that charge is pure waste. Send us the bill: the audit is free, and we'll tell you straight what to cut.
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