  We investigate theoretically the use of non-ideal ferromagnetic contacts as a
mean to detect quantum entanglement of electron spins in transport experiments.
We use a designated entanglement witness and find a minimal spin polarization
of $\eta > 1/\sqrt{3} \approx 58 %$ required to demonstrate spin entanglement.
This is significantly less stringent than the ubiquitous tests of Bell's
inequality with $\eta > 1/\sqrt[4]{2}\approx 84%$. In addition, we discuss the
impact of decoherence and noise on entanglement detection and apply the
presented framework to a simple quantum cryptography protocol. Our results are
directly applicable to a large variety of experiments.
