How does my stereo predict incoming cell phone calls?

If my stereo is on and my cell phone is in the living room, a second or two before my phone rings, I hear a low hum through the stereo system. Ususally it’s on, and silent, as it is also the sound system for my computer.

Obviously, there’s some interference going on. But there’s zillions of cell phone signals zipping through my apartment constantly. So I’ve concluded that my cell phone is transmitting before activating the ringer, to cause this interference.

Why would it do this? I’ve read that cell phones periodically transmit to the nearest cell to be “registered” at that location, but I get no interference from these transmissions. Only just before an actual incoming call.

What’s the deal?

The protocol to connect a cell phone call is a handshake that occurs between the phone and the switch when making a connection. I don’t remember the technical details, but it’s something like this:

“Hey phone, you’re supposed to be there, based on the last time we checked. Are you?”
“Yeah, I’m here. What’s up?”
“I got a call for you. Are you ready to take a call?”
“Yeah, fire away”
“OK, here’s the data you need to get started. Start ringing and I’ll connect you when someone answers.”

My Nextel phone is notorious for intefering with my stereo, my car stereo, and my computer speakers. I get pulses of static just before it rings, or sometimes just at random. I haven’t experienced this with two other carriers (I think Nextel’s transmission technology is unique).


It does so, even if there’s no incoming calls. Most phones “roam” as the technical term is (at least with GSM) at intervals to let the network know where it’s at.

Youäll notice that when you turn on your phone every morning at home, it connects pretty quickly. However, if you turn of your phone, say when going on a flight, turning it on again usually makes it search for several seconds, maybe up to 30. That’s when your phone is roaming and yelling: “I’m here, I’m here.” The network had you placed in another city, last time you turned it off.

I don’t know about the US, but here, cell phones are a big no no in hospitals. Some guy thought up the idea (and maybe got a patent) to put up speakers around the place, but not playing anything back. When cell phone was on, the d-d-wum-d-d-wum in the speakers would rat out the offender, getting staff to make him turn it off.

I can’t beleive you guys in the US pay for incoming calls to the cell phone. Here, as long as you’re using your own operator, all charges go to the person dialing.

I got told it’s the nearest cellphone tower checking to make sure it’s still the nearest tower as before.

Though I think that’s the same as what CookingWithGas said.