Haltech Rare Earth Magnets (REM) are extremely strong for their size and have the highest resistance to demagnetization of any permanent magnet known to man. Haltech REM are rated to the highest temperature you can get which makes them ideal for use in an automotive application - beware these suckers are strong! Haltech REM are polarized and designed to be used exclusively with Haltech's own S3 and S4 Dual Channel Hall Effect Sensors. Price is per magnet.