To cause a batch file to beep for attention, you need to send a BEL character.

The easies way to do this is to open a CMD prompt and CD to a folder in your path. Then type:

edit bell.bat                              @echo<space><CTRL+P><CTRL+G><ENTER>                              <ALT+S>           (Saves bell.bat)                              <ALT+X>           (Exits edit)
NOTE: <> indicates that you type the key(s) within the <>.

            CONTROL CHARACTERS

   Decimal  Hexadecimal  Character  Mnemonic                                 00       00           NUL        ^@                                 01       01           SOH        ^A                                 02       02           STX        ^B                                 03       03           ETX        ^C                                 04       04           EOT        ^D                                 05       05           ENQ        ^E                                 06       06           ACK        ^F                                 07       07           BEL        ^G                                 08       08           BS         ^H                                 09       09           HT         ^I                                 10       0A           LF         ^J                                 11       0B           VT         ^K                                 12       0C           FF         ^L                                 13       0D           CR         ^M                                 14       0E           SO         ^N                                 15       0F           SI         ^O                                 16       10           DLE        ^P                                 17       11           DC1        ^Q                                 18       12           DC2        ^R                                 19       13           DC3        ^S                                 20       14           DC4        ^T                                 21       15           NAK        ^U                                 22       16           ETB        ^W                                 23       17           SYN        ^V                                 24       18           CAN        ^X                                 25       19           EM         ^Y                                 26       1A           SUB        ^Z                                 27       1B           ESC        ^\[                                 28       1C           FS         ^\                                  29       1D           GS         ^\]                                 30       1E           RS         ^^                                 31       1F           US         ^_