diff --git a/3-list_imsi.sh b/3-list_imsi.sh
index abe01e2..4e87bdf 100755
--- a/3-list_imsi.sh
+++ b/3-list_imsi.sh
@@ -1,2 +1,3 @@
 #!/bin/bash
+echo "Usage: ./3-list_imsi.sh ARFCN-freq (ex. 935.4M)"
 grgsm_livemon_headless -f $1