5 GB
UK 4-network
£8.85a month per active SIM, ex VAT
Order 5 GB4G backup for a broadband line
Plan a router failover connection, choose which traffic it carries and test the applications you need during an outage.
Use a compatible router to switch essential traffic from broadband to a 4G data SIM when the main line is unavailable. Start by deciding what must keep working, then size the mobile allowance and test the router's failover behaviour. UK 4-network 5 GB is a starting plan at £8.85 per active SIM per month, not an unlimited replacement for the line.
The SIM provides mobile data. Your router decides when to use it and which devices can send traffic through it. Check that the router supports the failover arrangement you want before ordering or changing the network.
Define the essential workload
List the services you need during a broadband outage. For a small shop, that might be a payment terminal and access to an order system. For a home office, it may be a particular work application. Treat software downloads, cloud backups, streaming and guest access as separate decisions.
Where the router supports it, configure the backup connection to carry only the traffic you have budgeted for. Otherwise all connected equipment may compete for the same allowance. A large plan does not remove the need to understand what the router carries.
Consider how long you want the backup to cover. Estimate a short outage and a longer one rather than assuming the main line always returns quickly. If you cannot keep the expected workload within 5 GB, reduce it or discuss the requirement through contact before treating this plan as sufficient.
A worked allowance calculation
Suppose your essential applications together use an assumed 100 MB per hour during an outage. These are example inputs, not measured figures for any particular application.
| Item | Example calculation | Data |
|---|---|---|
| Essential traffic for one working day | 100 MB × 8 hours | 800 MB |
| Three such outage days | 800 MB × 3 | 2,400 MB |
| Four planned connection tests | 50 MB × 4 | 200 MB |
| One allowed update | Assumed download | 500 MB |
| Total planned use | Sum of the above | 3,100 MB |
For planning, treating 1 GB as 1,000 MB puts this example at 3.1 GB. A 5 GB allowance gives room above that estimate, but the spare space is not a promise about unmeasured traffic. Replace the assumptions with usage from your own router and SIM.
A webcam, update or staff download added later changes the calculation. Read how much data a device needs and keep a note of which applications the estimate includes.
Install and test the mobile link first
Install a compatible physical SIM or eSIM and activate it in the ThingSIM portal when you are ready to test. Copy the APN shown against that SIM into the router. Setting up a 4G router covers the initial connection before failover rules are added.
Try the intended router position and enclosure, then test the actual essential applications over mobile data. UK 4-network includes O2, Vodafone, Three and EE and uses whichever is strongest where the device is. Test at the site rather than assuming that the same position works as well for broadband equipment and mobile reception.
Keep the SIM active while it is expected to provide standby service. An unused spare can remain inactive, but a paused SIM is not a ready mobile connection for the router to use during an outage.
Run a controlled failover test
Choose a suitable time and tell anyone using the connection. Follow the router manufacturer's procedure to simulate loss of broadband. Confirm that the router selects mobile data, then test each essential application from the device that normally uses it.
Restore broadband and confirm that the router returns to the intended connection. Record what happened and whether anyone needed to reconnect an application. Do not assume that every existing application session continues unchanged when the router changes connections.
Repeat the test after meaningful changes to the router, mobile settings or essential applications. The router failover sector page provides the use-case overview. Keep your written test short enough that another person can run it when you are unavailable.
Watch the allowance during an outage
The portal shows SIM usage. At the allowance limit, the SIM pauses instead of charging overage, so check it during extended outages. If you are on a smaller plan, an immediate upgrade costs only the difference for the rest of the month. At 5 GB, the largest listed allowance, you need to wait for the reset. Plan for that limit before relying on the connection.
For automated monitoring, usage webhooks explains notifications, including thresholds at 80% and 100%. Developers can find the events in notifications. Agree who will act on an alert while the main connection is down.
Common questions
Can I leave the backup SIM paused until broadband fails?
A paused SIM cannot provide the ready connection your failover router needs. Keep it active while it is expected to serve as backup.
Is 5 GB unlimited backup broadband?
No. It is a monthly allowance, so estimate outage traffic and limit optional use where your router allows it.
Does ThingSIM configure my router's failover rules?
The SIM supplies connectivity. Use the router manufacturer's instructions or your network installer to configure and test its failover behaviour.
Recommended plan
UK 4-network, 5 GB a month
Roams across all four UK networks and uses whichever is strongest where the device is.
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