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If you have a Windows 10 PC that is connected to modem you can check the security type going to the security tab of the Wireless Adapters Wireless properties. If you install the WiFi analyzer by Matt Hafner from the Windows store this will display in detail the Encryption method and Authentication used
If you have an Android device you can use the Access points tab of the WiFi Analyzer by Abdelrahaman M, Sid to show what encryption is used.