Chip Hacking Help

I have a card with a chip on it that requires overwriting via a chip reader.
Where can I purchase a reader that overwrites?

Hypothetically, if it was a building laundry card.

You pretty much answered your own question.... Search chip reader/writer (can also look on the Dnet) etc. A device that reads only (reader like you said)...can read only and not write or "overwrite"...therefore you need a reader/writer. easy thing to research and get. I cannot provide any specifics as i do not encourage or condone any unethical/illegal activities etc as this topic can easily be considered or seen as fraud or similar. For legal purposes, this post should give you a boost into your research in getting what you want to do. Also, hypothetically speaking of course, if it's a laundry card (it's a track 1 on the mag strip)...hope this helps