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Seismometers, seismographs and seismograms are terms which are often interchanged. They are all associated with earthquake detection. To be precise, a seismometer is a sensitive instrument which sits on or in the ground and detects earth movements or vibrations. The seismograph records the motion detected by the seismometer. The seismogram is the actual record of the motion.
Early seismographs used mechanical devices to detect and amplify earth movements, and these were built into the recording instrument. By the late 1800's electromechanical seismographs became practical. The seismometer could send an electrical signal to a seismograph located away from the detector. Today, highly sensitive electronic seismometers are used to detect earth movements. The data from seismometers can be converted to digital data and transmitted to digital recorders. The resulting seismogram can be recorded on paper, disk and displayed on a computer screen.
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 The Maryland seismic network uses digital seismic records for earthquake detection. A visual record of our data can be displayed in several ways. Our online helicorder record shows a daily record of seismic activity, and is updated every 5 minutes. The Labin Online Seismograph uses Java technology to display a near real-time seismogram. Visually, this is somewhat closer to what you might see if you were looking at a mechanical seismograph. There is a slight delay (about 5 minutes) between the time motion is detected and displayed. This is due to the various steps need to process and transmit the data to your computer. See the Seismograph Help Page for more information about the online seismograph.
For another example of an online seismograph, see "Mori ,an Internet-based earthwork" from Berkeley, CA.
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Maryland Seismic Network