If you want to purchase the Wired DCI for use on your iDA- head unit there is a chance the head unit will "miss" commands or stop responding to commands if the head unit "display dimmer" feature is activated. This is a problem with the head unit, not the DCI, and originally started on the Alpine iDA-X001. The X001 worked fine as long as you used BLUE button illumination (dimmed or not) or used RED but never dimmed it. But the combination of RED and DIMMED caused the head unit to stop responding to commands on the wired remote control line. This issue does not affect the IR remote control functions, only the wired remote control input.
Update June 2009 - It seems this problem affects fewer of the 2008 and 2009 head units than it did the first production year for the iDA series. Some Alpine owners have recently reported their head units never miss a command, others say it only occasionally "skips". Newer head units have been reported to sometimes have the problem on BLUE illumination too, though it seems to be much less frequent.
Original Information from 2007 - Some head units miss more than others, as I've had customer complaints about "sometimes missing commands" and others report it "completely fails" when the dimmer is activated. I purchased an iDA-X001 for testing and it turned out to be one of the relatively good ones and rarely misses commands when RED and DIMMED. But is does miss them occasionally and I discovered the fastest way to test for "misses" is to hold the VOLUME button and run the volume up or down for the full range, which on this head unit requires 80 commands. Out of those 80 my head unit will miss one or two commands, but it will ONLY miss them if the buttons are set to RED and DIMMED. When set to BLUE or NOT DIMMED it never misses commands.
Alpine's response - Initially Alpine tech support said the problem was the "interface" (meaning the DCI). After replacing the DCI on several customer's systems (one was changed twice) and the problem remained they suggested to one customer that he change the head unit. After the head unit was changed and the problem remained, Alpine tech support told me the only "approved" interface device was the PAC unit and suggested the real problem was, (again) the DCI. So I purchased a PAC SWI-ALP unit to use on my iDA-X001 and guess what - it has the same problem, only worse. I notified Alpine tech support that their "approved device" didn't work either but they still would not admit it's a head unit problem and would not put me in touch with their engineers. I'm out of options, but maybe if enough customers complain they will do something.
In my testing the PAC unit misses MORE commands than the DCI does, sometimes as many as 6 or 8 missed commands during a single run up the volume range. See this video (3MB mp4) using the PAC unit and watch for when the volume bar graph pauses on the way up or down. The first part of the video is with RED buttons (with misses), then I change to BLUE and do another test and you'll see zero missed commands. If you turn the volume up high when playing the video you will also hear the beeps when the head unit misses a command (it beeps because it thinks the commands stopped and when they start again you get a beep).
I also learned that the PAC unit does not send a "clean" signal to the head unit, at least not compared to the DCI. Maybe that's why it misses more than the DCI does. I took these screen shots to illustrate that the DCI is definitely not sending a bad or inferior signal to the head unit. The signal should be perfectly straight with no rounded corners, but you can see the rounded bottom edges on the PAC signal and the extra lines and "clutter" on the top half, which are high-frequency signals that were not effectively filtered out before sending the command to the head unit. By comparison the DCI command is "picture perfect".