find where number changes in a matrix

I have a matrix of +1 and -1 values. I want to find where the number flips from 1 to -1 or vice versa where the change is a change from column to column.

X=[...
1  1  1  1;
1      -1  1  1;
1  1  1      -1;
1  1  1  1]

the answer should be [2,2],[2,3]and [3,4]. I tried

find(diff(X)==2);
find(diff(X)==-2);

Any help is appreciated

Answer 1

[Cedric]

 >> [r,c] = find(diff(X,1,2)) ;
 >> loc = [r, c+1]
 loc =
     2     2
     2     3
     3     4

Answer 2

[the cyclist]

One way:

[i j] = find(abs([zeros(4,1),diff(X,[],2)])==2)