  We study transitions of a particle between two wells, separated by a
reservoir, under the condition that the particle is not detected in the
reservoir. Conventional quantum trajectory theory predicts that such no-result
continuous measurement would not affect these transitions. We demonstrate that
it holds only for Markovian reservoirs (infinite bandwidth $\Lambda$). In the
case of finite $\Lambda$, the probability of the particle's interwell
transition is a function of the ratio $\Lambda/\nu$, where $\nu$ is the
frequency of measurements. This scaling tells us that in the limit
$\nu\to\infty$, the measurement freezes the initial state (the quantum Zeno
effect), whereas for $\Lambda\to\infty$ it does not affect the particle's
transition across the reservoir. The scaling is proved analytically by deriving
a simple formula, which displays two regimes, with the Zeno effect and without
the Zeno effect. It also supports a simple explanation of the Zeno effect
entirely in terms of the energy-time uncertainty relation, with no explicit use
of the projection postulate. Experimental tests of our predictions are
discussed.
