A:Answer If by "plug in" you mean, plug into a wall socket for power, then, yes, they both must plug in. If you're asking about "plug in" and mean plug into your modem, then no -- only the wifi router plugs into the modem. The other device (satellite) needs to get power from a wall socket but gets its internet signal from wifi from the router. The pair of devices worked very well for my wife & I in our house, but I ended up deciding I needed a second satellite (and couldn't buy just a single satellite to add to my router + satellite pair I'd gotten from BestBuy, so I opted to buy it elsewhere). Loving the speed from my three-unit mesh, though -- downloads usually around 400-450 mps for cable-based 400 mps service!!)