  The drift in the redshift of objects passively following the cosmological
expansion has long been recognized as a key model-independent probe of
cosmology. Here, we study the cosmological relevance of measurements of time or
redshift derivatives of this drift, arguing that the combination of first and
second redshift derivatives is a powerful test of the $\Lambda$CDM cosmological
model. In particular, the latter can be obtained numerically from a set of
measurements of the drift at different redshifts. We show that, in the
low-redshift limit, a measurement of the derivative of the drift can provide a
constraint on the jerk parameter, which is $j=1$ for flat $\Lambda$CDM, while
generically $j\neq1$ for other models. We emphasize that such a measurement is
well within the reach of the ELT-HIRES and SKA Phase 2 array surveys.
