  The ALICE collaboration is proposing a completely new detector, ALICE 3, for
operation during the LHC Runs 5 and 6. One of the ALICE~3 subsystems is the
Muon IDentifier detector (MID), which has to be optimised to be efficient for
the reconstruction of $J/\psi$ at rest (muons down to $p_{\rm T}\approx1.5$
GeV/$c$) for $|\eta|<1.3$. Given the modest particle flux expected in the MID
of a few Hz/cm$^2$, technologies like plastic scintillator bars ($\approx1$ m
length) equipped with wavelength-shifting fibers and silicon photomultiplier
readout, and lightweight Multi-Wire Proportional Chambers (MWPCs) are under
investigation. To this end, different plastic scintillator paddles and MWPCs
were studied at the CERN T10 test beam facility. This paper reports on the
performance of the scintillator prototypes tested at different beam momenta
(from 0.5 GeV/$c$ up to 6 GeV/$c$) and positions (horizontal, vertical, and
angular scans). The MWPCs were tested at different momenta (from 0.5 GeV/$c$ to
10 GeV/$c$) and beam intensities, their efficiency and position resolutions
were verified beyond the particle rates expected with the MID in ALICE 3.
