Go to the webpage of your Smile P1 via connect.plugwise.net. Check the settings for your firmware version.
Smile P1 (V1): The first generation has an external antenna and has firmware version 2.1.7 - 2.1.17.
Smile P1 (V2): The second generation has no external antenna and has firmware version 2.5.4 - 2.5.9.
Smile P1 (V3): The third generation has been delivered since July 2019. It has no external antenna and has firmware version 3.3.6 and higher.