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Not sure if it's the Lexus key fob or not but if there's any external metal showing, try a thin magnet telescope tool. You can pick one at any tool supplier.
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Take a wire clothes hanger and contort it however you need in order to get them. You may have to try from the back floor board (put seat all the way up) or from the front floor board (put seat all the way back). I've done this a few times and find being in the back floor board is most successful.
In addition to the grabber shown by kitabel, there is also one with a magnet at the end. It's great for picking up light metal objects like keys, screws, nails, nuts, bolts, etc.