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Let's say I have something akin to a garage door clicker. How can I discover the frequency and message it sends with no other information on the device? I want to decode this to the electrical signal and build my own device to retransmit it.

Is something like this good?

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  • \$\begingroup\$ I assume you have done the obvious and dismantled the device, looking for any convenient stickers or PCB markings that might tell you the frequency. :) \$\endgroup\$ – Li-aung Yip Apr 28 '14 at 15:30
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    \$\begingroup\$ Odds are you can find your answer by Googling it, if someone else has done it before, else this is one of those "if you have to ask..." questions. What you want to do will take expensive equipment and skills a hobbyist won't have. RF design is not trivial. \$\endgroup\$ – Matt Young Apr 28 '14 at 15:30
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    \$\begingroup\$ That won't do what you're looking for. That's a land mobile radio receiver which only listens to certain devices in the 800 MHz range. Most garage door openers operate at around 300-400 MHz. If there are any marking on it you can look at the FCC filing for the device to get more detailed information. \$\endgroup\$ – Ryan Johnson Apr 28 '14 at 15:35
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    \$\begingroup\$ For wireless devices sold in the USA, the frequency of the device can be found by searching the FCC ID. \$\endgroup\$ – Luke Rehmann May 12 '16 at 17:47
  • \$\begingroup\$ The "RTL-SDR" dongles work well in the frequency range of many of these remotes, excepting the newer and less common 2.4 GHz variety. But beware that a properly designed garage door system will have remotes which are unclonable by anyone. Unless there are design faults, the only way to add a remote will be to introduce the new one with a unique code of compatible form to the receiver - of course, many real world systems do have design faults. \$\endgroup\$ – Chris Stratton Oct 19 '17 at 15:01
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If you have an old TV tuner around with you might get lucky matching the VHF/ UHF channel to the common narrow band transmitters or harmonics, but newer spread spectrum and rolling code encryption garage door openers are very secure. It may result in some long nights scratching your head without some experience using TV tuners as spectrum analyzers with a scope. It may lead to quit and start another profession. Or it may inspire you to learn how to use a TV tuner as a scanner using a loop antenna for near field signals.

First match the technology of the chips inside or brand or at least learn about garage door openers.

http://en.wikipedia.org/wiki/Garage_door_opener

I once proposed to Chrystler as a second source company, when they were buying from Delphi , who bought the technology for garage for openers for over a billion $ from this other company due to a hundred patents and muchos experience. So this experience is not free nor easy.

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For wireless devices sold in the USA, the frequency of the device can be found by searching the FCC ID.

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  • \$\begingroup\$ This is quite often the most effective answer. \$\endgroup\$ – Chris Stratton Oct 23 '17 at 0:12

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