[http://graphics.x10.com/images6/mr26a_parts_350x263_72.jpg][http://www.x10.com/products/x10_mr26a.htm]
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Wireless (RF) sensors that attaches to a PC through a serial port.  The unit decodes the RF signals and X10 provides software that will control X-10 devices, MP3 players, etc.

X10 also makes some combination RF/IR remotes that can sent more than just the typical light commands to the mr26a (example UR47a, UR81a, ...).  These map each button of the remote to a signal that is decoded by the mr26a.  Below is a little application that read the mr26a and displays the button pressed on the RF remote. (This code is based off the [How to read the serial port, and display in hexadezimal] example)
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 # Please send any comments/bug reports to
 # Michael Jacobson (mpjacobson2000@yahoo.com)
 # tested with Tcl/Tk 8.4b3
 
 ### Constants
 set baudrate   9600
 set parity     n
 set databits   8
 set stopbits   1
 set comport 	com2:
 
 ### Button Mapping
 set dlable {POWER PC TITLE SUBTITLE DISPLAY RETURN MENU EXIT \
             LEFT UP RIGHT DOWN OK PLAY STOP SKIPPREV \
             SKIPNEXT REWIND FORWARD PAUSE RECORD RECALL ONE TWO \
             THREE FOUR FIVE SIX SEVEN EIGHT NINE ZERO \
             ABSWITCH ENTER CHANNELUP CHANNELDOWN VOLUMEUP VOLUMEDOWN MUTE LIGHT1ON \
             LIGHT2ON LIGHT3ON LIGHT4ON LIGHT5ON LIGHT6ON LIGHT7ON LIGHT8ON LIGHT1OFF \
             LIGHT2OFF LIGHT3OFF LIGHT4OFF LIGHT5OFF LIGHT6OFF LIGHT7OFF LIGHT8OFF ALLLIGHTSON \
             ALLLIGHTSOFF}
 set dcode  {EEF0 EED4 EED6 EED4 EE3A EED8 EEB6 EEC9 \
             EED2 EED5 EED1 EED3 EE52 EEB0 EE70 EE00 \
             EE00 EE38 EEB8 EE72 EEFF EEF2 EE82 EE42 \
             EEC2 EE22 EEA2 EE62 EEE2 EE12 EE92 EE02 \
             EEBA EE52 EE40 EEC0 EE60 EEE0 EEA0 6000 \
             6010 6008 6018 6040 6050 6048 6058 6020 \
             6030 6028 6038 6060 6070 6068 6078 6090 \
             6080}
 
 ### G U I
 text .t1 -width 85 -font {courier 8 } -tabs {3c 6c 9c 13c left}
 pack .t1 -side top -anchor nw
 button .b1 -text Exit -command exit
 pack .b1 -side bottom -anchor nw -fill x -expand true
 wm title . "X-10 RF Signal to Hex Convertor ($comport)"

 ### M A I N
 .t1 tag configure underline -underline true
 .t1 tag configure bold -font {courier 10 bold}
 .t1 tag configure finsih -font {courier 6}
 .t1 insert end "\tRead $comport $baudrate, Parity=$parity,\
     Databits=$databits, Stopbits=$stopbits\n\n" {underline bold}

 ### Procedures
 set olddata ""
 proc rd_chid {chid} {
 	global olddata oldtime
   	set newtime [clock clicks -milliseconds]
   	set msg [read $chid]
   	.t1 insert @0,0 . ;#data received
   	if {[string equal $msg $olddata]} {
   		if {[expr $newtime - $oldtime] < 200} { 
   			set oldtime $newtime 
   			return ;# debounce the button
   		}
   	}
   	set oldtime $newtime
   	set olddata $msg
   	set listOfLetters [split $msg {} ]
   	set serialIPinHex ""
   	foreach iChar $listOfLetters {
      	       scan $iChar "%c" decimalValue
       	       set serialIPinHex "$serialIPinHex [format "%02X" $decimalValue ]"
   	}
        set out_rfdata "[lindex $serialIPinHex 2][lindex $serialIPinHex 3]"
   	set result_updaterf [rfdecode $out_rfdata]
   	.t1 insert @0,0 "rf data sent:\"0x$out_rfdata\", remote code:\"$result_updaterf\"\n"   
 }

 proc rfdecode {data} {
 	global dlable dcode
  	set fnd [lsearch $dcode $data]
	if {$fnd == -1} {
  		set output "Code not found : $data"
  	} else {
  		set output [lindex $dlable $fnd]
  	}
  	return $output
 }
 
 proc open_com {} {
   global com comport baudrate parity databits stopbits
   set com [open $comport r+]
   fconfigure $com -mode $baudrate,$parity,$databits,$stopbits \
      -blocking 0 -translation binary -buffering none
   fileevent $com readable [list rd_chid $com]
 }
 
 proc Exit {} {
 	global com
	close $com
	exit
 }
 wm protocol . WM_DELETE_WINDOW {Exit}

 open_com