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How Do I Filter Phone Calls on a Land Line?
An anonymous reader asks: "I have a telephone on a plain old land-line, with the option of subscribing to caller-id.
I would like to filter incoming phone calls, diverting them to either the handset or answering machine, based on whether the caller-id matches a list of trusted phone numbers.
Considering that many of today's land-line telephone handsets can display caller-id and store a list of favourite phone numbers, I don't think this is technologically difficult.
AI am not interested in: subscribing to a service provided by my telephone company. I would prefer the filtering occurred on my side of the phone line, or implementing a software solution on my PC. Frankly, that is overkill, and I don't want my PC turned on permanently. I would prefer something like a small, solid-state hardware device. Is there any such thing available?"
http://www.privacycorps.com/products/?id=20
Well the obvious answer (at least to me) is Asterisk. If you don't want a "computer running all the time" build a small box, well.... tuff. Think Mini-ITX. You can put a small HD in in, and put it in a small case. If its only "diverting" calls it doesn't need much power or storage space at all and wouldn't draw much power (also, if you do it right - it could be all passive cooled).
Also - I'm sure no one wants to spend _that much time_ setting up Asterisk, so use TrixBox (Formely Asterisk@Home) instead.
snowulf.com
If you weren't such an asshole/idiot, you'd notice that someone else has indicated that such a device does exist: http://www.privacycorps.com/products/?id=20
To lead off, a suitable software/computer prototype can be made with a computer and modem. Most modems can be put into a "report caller ID" mode. Make some simple C software to listen ot the serial port, and control the relay going to the regular phones using the parallel port.
Once you have a suitable software prototype, use a PIC or AVR to talk to the modem and control the relay. At this point you've got an easy, simple system that does what you want it to do - but you've probably got to update it tediously by reprogramming the micro. Add an LCD and keypad and you can do it by hand.
Alternately use a Rabbit core module with ethernet and rabbit web ( http://www.rabbit.com/ I work for them) and keep the list up to date over the network. It would also give you quite a bit more power with less work than the PIC or AVR, but it's more expensive. As always one trades fastcheapgood.
I'd leave the answering machine always connected to the phone line. Block the ring from the other phones until the caller ID is decoded. It gives you one less ring to answer the phone in, but that's a price you may just have to pay.
-Adam
Looks like this Uniden handset has the functionality you mention: Uniden TRU9465-2 Expandable Cordless System with Dual Keypad and Call Waiting/Caller ID and Extra Handset and Charger
I had set up vgetty to answer calls after a number of rings that was based on the caller-id information, but that requires a modem whose voice capabilities are supported on linux. The idea was that 'Unknown Caller', etc. went straight to the voicemail, but everything else was allowed to ring four times. It's a simple and proven method.
Fnord.
My AT&T E5965C does exactly that. It's about $120 if you can catch it on sale.
Here it is at Amazon
Just remember that anytime you're talking on a cordless phone, you're using a radio transmitter. While that might seem like a painfully obvious thing to say, it's amazing how many people don't get the connection between "cordless telephone" and "anyone with a scanner can hear everything I'm saying." If you don't believe me, find any good radio that has wideband receive and try searching from around 46.6-50 MHz for the older phones and 900-928 MHz for the new ones. I don't have a receiver that goes to 2.4GHz but I have no doubt that if you did, you'd hear lots of people up in that band, too (although decoding the digital ones might be non-trivial).
Whenever somebody brings up email privacy I just laugh -- we'll work on email encryption right after we figure out a way to convince people that broadcasting their conversations miles in every direction probably isn't a great idea.
Anyway, I recommend that anybody who uses a cordless phone as their primary means of communication should borrow a scanner for an evening and play around with it--see if you can find the frequency of your own unit. I know I'll never discuss anything sensitive on one ever again.
"Ladies and gentlemen, my killbot features Lotus Notes and a machine gun. It is the finest available."
The Caller-ID information is sent between the first and second ring, so the only way to avoid ringing is to drop the first ring 100% of the time. On the occasions where you do want to talk to someone, the time left to get to the phone is that much shorter.
I have an AASTRA talking Caller-ID box in my house. It does a great job of managing the phone. If the caller has intentionally blocked their Caller-ID information then it automatically answers after one ring and tells them I don't accept blocked calls (which are inevitably from telemarketers) and they should call back with Caller-ID enabled. For the rest, it speaks the phone number so I know who it is before I get to the phone. If it's someone I don't want to talk to then I just let it ring until the answering machine cuts in. It supports blacklisting so that people who annoy me don't even get to leave a message. One interesting feature is that I can record a short audio clip and have it matched to a specific name or number so that it will play that audio clip instead of speaking the number. That's a great help with things like payphones which I will always want to answer no matter what the number is (my telco sends "payphone" as the Caller-ID name).
Years ago (when I still had landlines) I had a box that intercepted all incoming calls without allowing the phones to ring. It delivered a simple message "Please enter your desired extension, or, if you do not know the extension, please dial "O" or wait on the line. Bleep!"
People were given one of several numbers to enter: 472 for family, 333 for work, 505 for businesses, for example.
472 always rang through with a particular ring, 333 rang through with another, 505 it would allow through or not depending on how I set the switch, with yet a third ring style.
Anyone who didn't have a good three digit number went to the answering machine, with no audible ring on any phone.
It was simple and effective, and anyone with the proper code could get through from any touch-tone phone.
People never had any problem with my giving them an extension number, as in "Call me when my car is ready, 206 555 0293, extension 505.)
I don't know if anyone still makes that simple box, but it would be worth checking for...
--
Tomas
Just as one example, there is more to a caller then "good number" or "bad number". There are actually 3 choices on the machine: 1= do not send to answering machine and do not ring the phone. This would be the ex-wife option. 2= send to answering machine but do not ring the phone. This is the current wife option. 3= ring the phone first and if no answer then let them leave a message. This is the current girlfriend option.
Second, TIME and DATE are sent by caller ID, you don't set them in the machine! Arrgh!. I don't have the time or patience to retype the whole (badly written) user manual here, but after having this device for 8 months I bought a second one just to keep in stock in case the first one needed service I would have a spare. Having this box to keep dimwits from ringing the phone is almost as good as Sex. Now, when the phone rings, it is guaranteed that the caller is someone I want to talk to. That's as good as getting only love letters in the mail, no bills or tax forms or junkmail.
This is quite a first I've seen on an Ask Slashdot. Someone's question is a very detailed list of the specifications of what they want a technological solution for. That's almost a miracle in itself that the question made sense, was slightly challenging to answer and research, and didn't involve asking for legal advice. Most amazing of all was that someone actually provided a link to a device to purchase that seems to do exactly what was asked for and more. Bravo!
OK, everyone, the Ask Slashdot category has been redeemed this once. I ask all Slashdotters to study this occurrence and try to implement these features on future iterations of Ask Slashdot.
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