For those who want to put tracer functionality with the MadBull Airsoft Hop-Up LED module, it's now back in stock again as announced by Simon. No need to buy a separate tracer unit and battery. You can have this fixed on your hop-up unit and draws its power from your AEG battery.... "Finally, after 30 days waiting. The LED module is available again. Reserve yours as soon as possible before it is gone."