The $α$-determinant is a one-parameter generalisation of the standard determinant, with $α=-1$ corresponding to the determinant, and $α=1$ corresponding to the permanent. In this paper a simple limit procedure to construct $α$-determinantal point processes out of fermionic processes is examined. The procedure is illustrated for a model of $N$ free fermions in a harmonic potential. When the system is in the ground state, the rescaled correlation functions converge for large $N$ to determinants (of the sine kernel in the bulk and the Airy kernel at the edges). We analyse the point processes associated to a special family of excited states of fermions and show that appropriate scaling limits generate $α$-determinantal processes. Links with wave optics and other random matrix models are suggested.