How Does a Security Gate Use Your Cell Phone to Open?

[minger]

Security Gate + Cell Phone = ?

OK guys, I have a "how does this work" question. I just moved into a new apartment which has a security gate. Now, aside from a few traditional means of opening, it has a rather unusual method, which I cannot figure out how works.

My phone number was entered into some database/program. Now, if anyone pulls up to the gate, they call me, at which time I press the "9" button, and the gate opens.

Are cell phone calls that easy to monitor that they can simply set up some sort of receiver to "listen in" for that particular button tone? How do they know who the person at the gate is actually talking to?

 

[Averagesupernova]

Are you sure they don't have to call you from a specific phone at the gate? This sort of thing has been in place for years on apartments only they called your home phone.

 

[minger]

I'm positive. We tried it out when I moved in. My buddy was outside the gate, called me on his cell (there is no phone out there), I press 9, and a few seconds later the gate opens. For that matter, I've already seen a lot of delivery guys (pizza, etc) on Sundays and late nights waiting at the gate on their cell phone.

Attached to the entry "kiosk" (for lack of a better word), there is a box with an antennae poking out. So...I don't know much about any of this stuff, but I haven't been able to stop thinking about it.

 

[berkeman]

Very interesting. I googled some on the thread subject, but only found stuff for the fixed keypad systems already mentioned, and other systems that let you unlock gates directly on your cell phone.

What did you have to do to sign up for this feature? You must have had to give your landlord your cell phone or something? One possibility is that the outside antenna is the closest (shared among cell providers?) antenna, and picks up the call and handles the transaction. So it still would be relatively secure, since it's all through the cell providers' infrastructure.

You could try calling your cell provider's customer support line if you haven't been able to figure it out by asking your landlord...

Please let us know the answer. Very interesting question!

 

[dlgoff]

This doesn't tell how it works but ...

Elite Dial Code Telephone Entry for Perimeter Control
The Dial Code LC and VF telephone entry/access control systems offer the latest technology for safe, convenient access
in buildings with 25 to 1,000 tenants. The bright, easy-to-read, 2-line screen includes a built-in resident
directory for guests. Visitors can call and speak to any resident by simply entering the tenant’s 3-digit personalized code.
The tenant may then grant access by pressing a number on their telephone or deny access by simply hanging up.
Loaded with several standard and exclusive features, both Dial Code systems provide expandability to 31 remote
locations, audio “help” assistance for guests and a patented “double box” design for easier installation and programming.

http://www.gatesnfences.com/Access-Control-TelePhone-Entry-Intercom-Systems-Keypads/Elite-Dial-Code-Perimeter-Control-Telephone-Entry-System.html"

 

[berkeman]

This doesn't tell how it works but ...


http://www.gatesnfences.com/Access-Control-TelePhone-Entry-Intercom-Systems-Keypads/Elite-Dial-Code-Perimeter-Control-Telephone-Entry-System.html"

That sounds like the system that has a fixed station that the visitor uses, as opposed to the OP's system where apparently the visitor can use their own cell phone.

 

[MATLABdude]

Maybe I'm misunderstanding here, but are you sure they're not monitoring your calls (I'm presuming on your land line, routed through their hardware) instead of all cellphone users around your area?

Maybe I'm just naive, but I don't think there's a way to legally intercept cell phone calls in the US unless you're law enforcement / intelligence and, even then, have a warrant to do so.

EDIT: Actually, I'm not certain that they're allowed to intercept your land line calls either (without your permission, at any rate--that was probably in the lease/purchase agreement you signed)

 

[dlgoff]

That sounds like the system that has a fixed station that the visitor uses, as opposed to the OP's system where apparently the visitor can use their own cell phone.

Yea you're right. I misread about calling from the gate.

 

[skeptic2]

Are you sure they aren't first dialing a number for the apartment complex and then the number of the person's cellphone? I'm wondering if they might be relaying the call.

Does this work with all cell phones or just CDMA or just GSM?

I believe CDMA has three levels of encryption so intercepting a CDMA call is not trivial, however there are communication analyzers that can decrypt the calls. Using one for that purpose I would think would be illegal.

 

[minger]

What did you have to do to sign up for this feature? You must have had to give your landlord your cell phone or something?

All I did was give them my cell phone number.

One possibility is that the outside antenna is the closest (shared among cell providers?) antenna, and picks up the call and handles the transaction.

That's kind of what I was thinking, but it raises some security questions for me at least. What's to stop someone from sitting outside my place with one of these monitoring my incredible boring calls to my friends?

I will try asking someone to see what's going on exactly. I'm pretty sure the apartment management doesn't know, but perhaps they have a manufacturer/model or something I could look up.

 

[berkeman]

What's to stop someone from sitting outside my place with one of these monitoring my incredible boring calls to my friends?

My premise was that the antenna is owned by the cell providers, so it's no different from the antennas on the towers. It would have a connection into the cell providers' infrastructure, without any way to tap into that connection.

 

[minger]

OK, this question has been found...and I feel like a jackass.

It turns out that dlgoff pretty much had it nailed. You must call the residents from the kiosk. I asked my friend who helped me move in, to which he said:

Well...there was a guy behind me. I didn't see him, but I guess he could have swiped his card

What a disappointment, haha.

 

[DaleSwanson]

That's kind of what I was thinking, but it raises some security questions for me at least. What's to stop someone from sitting outside my place with one of these monitoring my incredible boring calls to my friends?

I see that you have your answer. But, I felt this was particularly relevant to your concerns about intercepting cellphone communications:

http://www.infernodevelopment.com/hacker-intercepts-cell-phones-defcon-1500-system

An ethical hacker named Chris Paget demonstrated live interception of GSM cell phones from AT&T and T-Mobile at Defcon Hacking Conference on Saturday. Despite concerns that he could be arrested or fined for illegally intercepting cell phone calls, he went ahead with the demonstration.

Paget used a $1,500 system to create a base station that tricks cell phones into thinking it's a legitimate cell tower, allowing the device to intercept even encrypted phone calls. Encrypted phone calls have no security because the rogue tower can simply turn off the encryption of the phones.

The device Paget created, called an IMSI (International Mobile Subscriber Identity) catcher, has already been used by law enforcement and intelligence agencies. The device entices cell phones in the area to ignore nearby cell towers and to use itself by providing a stronger signal.

After activating the device, 30 different cell phones connected to the device as Paget configured it to spoof an AT&T tower. Paget quipped "As far as your cell phones are concerned, I am now indistinguishable from AT&T. Every AT&T cell phone in the room will gradually start handing over [calls] to my network."

During the conference, Paget explains that such a device "used to be a million dollars, now you can do it with a thousand times less cost... If it's $1,500, it's just beyond the range that people can start buying them for themselves and listening in on their neighbors."

 

[minger]

I think I read that some time back on Slashdot. Scary...

 

[MacLaddy]

I am a member of my condo association, and we have been negotiating terms to install one of these gates. From what I understand the tenant has to have a hard line wired into their unit, and this is what's intercepted when the approval is given.

 

[minger]

This one doesn't do hard lines. I tried it the other day, it definitely calls my cell phone. It comes in as an 800 number, so I'm not sure if the box itself has some sort of calling plan or something like that. The people said that often times that can be a convenience if, for example, you happen to be out of the house and someone wants to come in.

 

[skeptic2]

So the keypad could be tied directly into a phone, which calls you. The receive side of the gate phone could have a detector for the DTMF tone for "9" which then opens the gate?