copy row to next free row on another spreadsheet on change - vba

Question

First off, I'm a noob when it comes to Macros and VBA, so please forgive me if I don't make sense.
I've got an Excel spreadsheet which is basically a list of users and their mobile phone numbers and some other bits (columns A-K are currently used) and it's ordered by rows.
What I need is a way of copying the whole row if I change a cell. So if I change the username, it copies the whole row of that user to the next blank row on a second sheet.
The purpose of this is to keep an audit trail allowing us to see who's previously used a number etc.
I found this: Copy row to another sheet in excel using VBA which is working as intended, but I can't for the life of me get it to a, copy the cells to the next free row, or b, not overwrite the existing entry.
This is the code I'm using:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim a As Range, rw As Range
For Each a In Selection.Areas
For Each rw In a.Rows
If rw.Row >= 2 Then
rw.EntireRow.Copy Sheet2.Cells(2 + (rw.Row - 2) * 3, 1)
End If
Next rw
Next a
End Sub
I'd really appreciate it if someone could help me customise it.
I'm using Excel 2010 on Win7.
Many thank in advance.

Answer 1

Typically the Intersect method is used to determine if the cell or cells receiving a change involve one or more columns that you are concerned with. You can add additional parameters; in this case, I've .Offset the Worksheet.UsedRange property down one row to make sure that row 1 is not involved.
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Columns(1), Me.UsedRange.Offset(1, 0)) Is Nothing Then
On Error GoTo bm_Safe_Exit
Application.EnableEvents = False 'not really necessary in this case but never a bad idea within a Worksheet_Change
Dim a As Range
For Each a In Intersect(Target, Columns(1), Me.UsedRange.Offset(1, 0))
If CBool(Len(a.Value2)) Then _
a.EntireRow.Copy _
Destination:=Sheet2.Cells(Rows.Count, 1).End(xlUp).Offset(1, 0) 'not really sure this is the correct destination
Next a
End If
bm_Safe_Exit:
Application.EnableEvents = True
End Sub
I've included a call to disable event handling for the duration of the Worksheet_Change event macro. While this is a critical step when the Worksheet_Change modifies values, it is not really important to incorporate here. However, it does not harm and is already in place in case you want to augment the Worksheet_Change to include something like a timestamp that would change the values on the worksheet.