  Rapid rotation is a fundamental characteristic of classical Be stars and a
crucial property allowing for the formation of their circumstellar disks. Past
evolution in a mass and angular momentum transferring binary system offers a
plausible solution to how Be stars attained their fast rotation. Although the
subdwarf remnants of mass donors in such systems should exist in abundance,
only a few have been confirmed due to tight observational constraints. An
indirect method of detecting otherwise hidden companions is offered by their
effect on the outer parts of Be star disks, which are expected to be disrupted
or truncated. In the context of the IR and radio continuum excess radiation
originating in the disk, the disk truncation can be revealed by a turndown in
the spectral energy distribution due to reduced radio flux levels. In this work
we search for signs of spectral turndown in a sample of 57 classical Be stars
with radio data, which include new data for 23 stars and the longest wavelength
detections so far ($\lambda \approx$ 10\,cm) for 2 stars. We confidently detect
the turndown for all 26 stars with sufficient data coverage (20 of which are
not known to have close binary companions). For the remaining 31 stars, data
are inconclusive as to whether the turndown is present or not. The analysis
suggests that many if not all Be stars have close companions influencing their
outer disks. If confirmed to be subdwarf companions, the mass transfer spin-up
scenario might explain the existence of the vast majority of classical Be
stars.
