How do I tell if RS1xx with RJ45 port is external temp sensor or RTD without label?

There is no difference in appearance between external temperature sensor and RTD version of RS1xx. One way to tell them apart is by using Sentrius mobile app in which temperature threshold can be set wider range in RTD than in external temperature sensor. The external temperature allows from -40C to 125C, and RTD version of RS1xx allows for significantly lower and higher temperature measurements.