Mmmm, after some tests I found a little problem.
Magnetic tape have a NSNSNSNSNSNSNSNS at one side of the tape.
Depending of the size of the tape the NS can be 1mm or 5 mm or maybe more distance from each other
I have tape there is only 2mm between N and S, so I have to find me other tape.

[youtube]http://www.youtube.com/watch?v=BiXQILw4aw4[/youtube]

BTW, some magnetic travel games have also small normal magnets, 3 till 5 mm.

Found it !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!

[youtube]http://www.youtube.com/watch?v=Otz7tCe_AAo[/youtube]

On the hallsensor there is the next codes.
1026
9868
A (looks gotic)
20E

This sensor is much to sensitive, but with a peace of magnetic tape behinde the sensor you can make it less sensitive.
With the magnet John use, the sensor is switching within 20 mm.
If I put a little peace of magnetic tape behinde the sensor it will be 3 till 5 mm befor the sensor is switching.

[youtube]http://www.youtube.com/watch?v=l8qT35UHK6E[/youtube]