A belt clip holster for cell phones, attached a retractable draw string, so that the phone is always attached to the clip, and subsequently the hip. The idea is to prevent accidentally leaving the phone somewhere, which happens to users who have minds that are always in some other place (like mine).
Some high-level specs:
1. Ideally, the phone would hang upside down at the hip, when in the retracted state. So the holster is attached to the beltclip at the bottom.
2. Both the clip and drawstring would have to be rather heavy-duty to hold up against being pulled dozens of times per day.
3. The holster would completely cover the phone, so the face of it should pick up on all the normal gestures used to interact with phone
4. Should have a button to disable retraction, so the thing isn’t tugging at you when you don’t want it to, like when using it as an actual phone that makes calls.
5. BONUS: Drawing or retracting drawstring charges phone.
EDIT: This actually comes pretty close to what I was thinking. The actual holster doesn’t seem too durable, as it is just a sticky backing that holds the phone, as opposed to a pouch. The cord and belt clip seem pretty lightweight, too. Also see this and this.