Novel semi-transparent silicon strip sensors (`ALMY sensors') have been developed
for the optical position monitoring systems of modern large-area
tracking detectors which allow to align several sensors along one laser beam.
The sensors are read out with custom-designed integrated electronics.
Crystalline silicon sensors are transparent for infrared laser beams and can be 
directly integrated on semiconductor tracking detectors.
Thin-film amorphous silicon strip sensors provide up to 90 per cent
transmittance for visible laser light combined with minimum beam distortion and
a typical position resolution of 1 micrometer over a sensitive area of several cm^2.
Transmittance and resolution of the amorphous silicon sensors is not affected by high
radiation doses. They are operated in a mode which minimises the degradation
of the sensitivity of the amorphous silicon under illumination such that
the sensor performance does not deteriorate.
ALMY sensors are in use or under investigation for vertex and tracking detectors 
of the ALICE, ATLAS, CMS, HERA-B, LHC-B and ZEUS experiments as well as for the
TESLA accelerator. The performance of the sensors is studied in several
real-size test stands.