We obtain novel constraints on new scalar fields interacting with Standard Model fermions through Lorentz-violating couplings, bridging searches for scalar particles and Lorentz-symmetry tests. These constraints arise from torsion-balance experiments, magnetometer searches, and an excessive energy loss in Red Giant stars. Torsion-balance experiments impose stringent constraints, benefitting from large macroscopic sources including the Sun and Earth. Magnetometer-based searches, which detect pseudo-magnetic fields through spin precession, offer additional limiting power to low-mass scalar fields. Meanwhile, observations of Red Giant stars place strong limits on additional energy loss mechanisms, extending these constraints to higher scalar mass ranges and a wider range of Lorentz-violating couplings. Combining data from laboratory experiments and astrophysical observations, this approach strengthens constraints on Lorentz-violating interactions and paves the way for future investigations into physics beyond the Standard Model.