There are a few ways that mobile telcos can know if you are using a modem instead of a smartphone:
* **IP address:** Every device that connects to the internet has a unique IP address. Mobile telcos keep track of the IP addresses of all the devices that connect to their network. If they see a device with an IP address that is not associated with a smartphone, they may assume that it is a modem.
* **Device type:** Mobile telcos can also identify the type of device that is connected to their network by looking at the device's IMEI number. The IMEI number is a unique identifier for every mobile device. Mobile telcos can cross-reference the IMEI number with a database of known devices to determine what type of device it is.
* **Data usage patterns:** Mobile telcos can also identify modems by looking at their data usage patterns. Modems typically use more data than smartphones because they are often used to connect multiple devices to the internet. Mobile telcos may also notice that modems tend to be used in different locations than smartphones.
If a mobile telco suspects that you are using a modem without paying for a tethering plan, they may send you a warning or even suspend your service.
It is important to note that mobile telcos' ability to identify modems is not perfect. There are ways to bypass mobile telcos' detection methods, such as using a VPN or changing the device's IMEI number. However, it is important to be aware of the risks involved in doing so.