The ability to sense the surrounding context makes modern smartphones a very powerful platform. Building efficient and robust mobile sensing applications, however, is rather challenging, as such applications need to ensure that the sensed data is at the same time as accurate as possible, but also acquired with as little battery energy used as possible. In this workshop, we will get introduced to the basic postulates of mobile sensing in Android. We will then focus on one of the most important sensing modalities –location –and through a two–hour hands–on lab learn how to efficiently build location–based services in Android using Kotlin programming language.