Whenever there is a deep excavation that is done prior to construction, the excavation has to be monitored prior to starting construction. This is a safety precaution. The depth at which any settlement may occur needs to be noted and this is where magnetic extensometers help. Reed Switches are used in Magnet Extensometer probes to monitor settlement and heave in foundations, excavations, dams, embankments, construction sites, mines and tunnels. The data collected by an Extensometer helps indicate the depths at which settlement are present. First, access pipes are inserted into the earth, and magnets are provided at every joint and coupling, at known, fixed distances. These joints are grouted to the soil and move whenever settlement occurs. The reed switch probe, coupled to a measuring tape is inserted from above. Each time the probe comes near one of the magnets at the junctions of the pipes, it triggers the reed switch and an indication is given. The depth can be read off the tape.