# Verify SIM Card
## Check SIM Card
The cellular router requires a SIM card to set up the internet connection over mobile networks. You can use data SIM cards or regular phone SIM cards on the 4G router.
Please check the factors below if the mobile interface is disconnected from the cellular networks.
* Please ensure the SIM card is **workable** and **activated**. You can test it on a mobile phone before inserting it into the 4G router.
* Ensure your SIM card is eligible to access the cellular 4G LTE networks.
* If it's a new SIM card, please follow the instructions from the mobile carrier and activate it.
* Please check the golden contacts on the SIM card.
* The SIM card is not workable if some golden contacts are broken or missing.
* If dirt is on the golden contacts, please [clean the SIM card](/ezr33/installation/insert-sim-card.md).
* The precise SIM cardholder has only one way to settle the SIM card correctly. If using a non-standard SIM card, please refer to the [insert SIM card](/ezr33/installation/insert-sim-card.md) to reinstall it.
* There are two SIM slots on the SIM card holder. The 4G router uses `SIM1` a slot by default. Please insert your SIM card in the `SIM1` slot. You can switch the router to use the SIM2 slot on the firmware. Go to `Network` > `Interface` > `Mobile`: `Edit` > `General Setup` > `Active SIM Card`.
{% hint style="info" %}
Please always turn off the router power before inserting or removing the SIM card. If you were inserting a SIM card when the router powered on, please run a hard reboot by reconnecting the PoE adapter.
{% endhint %}
## SIM Card Registration
After inserting a SIM card and the router is powered on, go to the [command-line](/ezr33/advanced/command-line.md) interface and use the command **`gcom`** to check the SIM card status and registration result.
### i. SIM READY
As the below standard example shows, if the SIM card is installed correctly, it should return **`SIM ready`** on line 2. If the SIM card is eligible to access the cellular network, you can get the registration result on line 4, which indicates the **mobile carrier's name**.
```
root@OutdoorRouter:~# gcom
Trying list of devices
SIM ready
Waiting for Registration..(120 sec max)
Registered on Home network: ""CHN-UNICOM"",7
Signal Quality: 28,99
```
### ii. SIM ERROR
If there is no SIM card installed the SIM card is installed incorrectly, or SIM card is non-workable, the return value shows `***`**`SIM ERROR***`,** like the example below.
```
root@OutdoorRouter:~# gcom
Trying list of devices
***SIM ERROR***
Check device port configuration.
Check SIM is inserted
Test SIM in a mobile phone?
```
### iii. REGISTRATION ERROR
If there is no cellular signal or SIM card that is not eligible to access the mobile network, it will also show SIM readiness, but the registration process will take `max 120 seconds` longer. The registration result will show **`Failed to register`** like the example below.
* Refer to [Signal Test](/ezr33/installation/signal-tests.md) to check if you have the 3G or 4G cellular signal reception.
* You can check with the *mobile carrier* if the SIM card is eligible to access 3G or 4G networks.
```
root@OutdoorRouter:~# gcom
Trying list of devices
SIM ready
Waiting for Registration..(120 sec max).............................................................
Failed to register
```
---
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