A processor measures characteristics such as the amplitude and/or delay of the reflected signal to determine...http://www.google.com.au/patents/US6363265?utm_source=gb-gplus-sharePatent US6363265 - Volume control for an alert generatorAdvanced Patent SearchPublication numberUS6363265 B1Publication typeGrantApplication numberUS 09/294,166Publication date26 Mar 2002Filing date19 Apr 1999Priority dat