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They are used as airbag-deployment sensors in automobiles , and as tilt or shock sensors . The index of refraction of seawater has long been used to make rough measurements of the salinity and density of seawater , but has proven difficult to utilize as the basis of a high precision sensor . Two astronauts primed the International Space Station ( ISS ) for future construction and installed a vital safety sensor to its exterior Thursday during a speedy spacewalk hundreds of miles above Earth . The comb-needle model enables us to investigate the cost of a spectrum of push and pull combinations for supporting discovery and query in large scale sensor networks .