We discuss how to detect entanglement in a large ensemble of spin-1/2 particles with collective measurements, using generalized spin squeezing inequalities. We present a method also for particles with a higher spin. Then, we consider the problem of detecting entanglement between two halves of an ensemble. In particular, we discuss detecting entanglement between two halves of the ensemble in Dicke states. Our methods consider experimental imperfections and have been tested in cold gas experiments.