You can get the security bits to open your TomTom rider at amazon.com for less than $10 with shipping, or they are even cheaper at a Harbor Freight store.
Below is a link to a video showing how to open a TomTom rider.
http://www.youtube.com/watch?v=j9_MF7EuLuQ
Stuart Ferguson
March 2009
If its the same as on a TT One then u need Torx 9
But with open tip. (hollow point)
Where to buy?
Any good hardware (tool) shop should have these.
Perhaps good idea to buy a set of torx "bits" because inside you'l find T6 sized ones.