RS-232 LED link Tester DB-9 Male to DB-9 Female

MFG Part Number: DB9-TERS
Test any male or female 9-pin RS232 connection using the status monitoring features of our DB9 Tester.
Key features
  • Tests any RS232 signal through its DB9 interface
  • LED status indicators for each RS232 serial signal
  • Small compact design for technicians on the move
  • Easy installation with Plug and Play
  • Light weight plastic housing for easy handling
Linux OSX 10 Windows Vista Windows XP
37 Review(s)

The DB9 Tester is the easiest way for you to test the connection on any male or female 9 Pin Serial connections. This adapter allows you to monitor the status of your connections by marking them with LEDS, which flash when there is activity on the pins. This device is easy to install, it features a Plug & Play Easy test RS-232 Host to Device link.

Pin Assignments:

  • DB - 9 / DB25 Pin assignment Pin1 / Pin8 : DCD <== IN
  • Pin2 / Pin3 : RXD <== IN
  • Pin3 / Pin2 : TXD ==> OUT
  • Pin4 / Pin20 : DTR ==> OUT
  • Pin5 / Pin7 : GND
  • Pin6 / Pin6 : DSR <== IN
  • Pin7 / Pin4 : RTS ==> OUT
  • Pin8 / Pin5 : CTS <== IN
  • Pin9 / Pin22 : RI <== IN

Additional Features & Specifications:

  • RS-232 DB-9 / DB25 Pin assignment No Power required
  • Standard RS-232 DTE & DCE Interface
  • Offers DB-9 Female & DB-9 Male Connectors
  • Easy to install , Plug & Play
  • OS Compatibility: Windows XP, 2000, 2003, CE, Vista, , and Windows 8 as well as Linux and Mac OS 10.X
  • RS-232 DTE connecter : DB9 - M
  • RS-232 DCE connecter : DB9 - F
  • Data rate : Up to 200 K bps
  • With GND & Shell Test's LED
  • Single / TTL out 1 - LED appear Green (V-)
  • Single / TTL out 0 - LED appear Red (V+)
  • Housing : Plastic
  • Weight : 55g
  • Dimensions (L*W*H) : 45 * 35 * 21 ( mm ) body
Part NumberDB9-TERS
I’m a happy camper

My products are fine. Unfortunately the device I needed them for isn’t. But the tester was just what I needed and the serial card is fine as well.

Great RS232 diagnosis tool

This is a great little device! As per the retention hex nut issue, this not a deal breaker. There are some excellent mods listed in the previous reviews. Or you can get a short serial cable on eBay for less than $2. Look for: RS232 DB9 9 Pin Male to Female Serial Port Cable Industrial Adapter 1.3M. Since this cable has thumb screws on both ends, it will act as an adapter.

Very nice


It works well - with a simple catch.
Flint Million

It does what it says it does and does it well. The LEDs give you a very clear indication of what's going on inside your serial cable. Only caveat is that this is designed to be a pass-through device (one side is male, one female) but both sides have the "female" retention screw holes. This means you can't plug it directly into pretty much anything, because pretty much all computer and even device serial ports also have the female screw holes. If you take the screw holes off with a hex driver, the metal shielding comes with them, so you end up with an unshielded connection. Your choice is either deal with that or get two M->F cables where both ends have the screw threads and put this in the middle. I ended up using a little Krazy Glue to glue the metal shield to the plastic casing, but without the screw holes it's probably not even doing anything anyway. Just a heads up - you may have to do a little hacking, or get extra cables with the correct ends, to get this to attach to anything.

Five Stars
jose luis ayala


Four Stars
Stacy Unruh

just using it for GPS signal but works great for that.

Five Stars
Mark Bitterlich

Does exactly what I needed it to do.

Five Stars
Alexandr Kazbanov

This small gadget saves a lot of time during installation or troubleshooting. I use it to test RS232 signal.

Five Stars
Mike Cline

It works great! Got it fast! All is GOOD!

Five Stars
Christopher Ryan

perfect for what i needed, good quality,

Works perfectly. Just what I needed to diagnose RS-232 ...
Steve Rohrer

Works perfectly. Just what I needed to diagnose RS-232 issues.

Product arrived on time, as described, no complaints.
DJR Computing Services

Product arrived on time, as described, no complaints.

Incredibly useful.

It's not perfect. As others have mentioned, if you remove the screw captures to use it (which is necessary for most applications), the ends fall off. However, I used small counter-sunk screws (the kind you get in little baggies with every piece of Extron gear ever) to keep it together, which does the trick. The device itself works well and is worth its weight in gold for anyone who installs a variety of rs232 controlled gear. If it were up to me, every technician I work with would carry one.

Five Stars
Michael Sablatura

Awesome! Worth every penny.

Neat device.
Amanda Melbourne

Works great - Very small. Neat tool for solving serial problems.

Neat device.
purple frog

Works great - Very small. Neat tool for solving serial problems.

Four Stars
duane d ellis


works as expected.
R Saulnier

works as expected. one star off ... had to replace stems with 4-40s screws .. very short ... see pictures

Five Stars
Ken Andrews

Great deal and exactly what I needed. Very satisfied.

Excellent diagnostics tool

Excellent diagnostics tool, expedites troubleshooting and repair of digital circuits. Will order additional, saved hundreds of dollars in lost time.

Amazon Customer

Not much to say about this little guy other then it works. I use it to test signal between control systems (AMX, Crestron) and the devices they control. One thing I would change is to make the pegs removable. Currently if you remove them then the metal around the input and output comes off. My workaround for this is to use gender changers on both end without the pegs.

Five Stars
Stuart Bercun


Five Stars
Stuart B


Excellent product, huge AV RS232 control troubleshooting timesaver.
AV Pro 77

As an AV professional this is an extreme time-saver for RS232/Serial control trouble shooting. It eliminates the guess work of whether TX & RX are swapped and saves you from pulling out your multi-meter and trying to juggle test leads and DB9 cables in your hands with a flashlight. My only problem that myself and others who have reviewed this product have seen is the lug screw issue preventing you from plugging it into a piece of gear such as a TV RS232 port to determine serial TX pinout. This is easily resolved by swapping them with screws. Excellent product, will buy again!!

serves its purpose
Gary Beckel

no information to tell you what light status or color indicates, lights poorly mounted, tilt in multiple directions was able to use it for my needs

Should be used by anyone making first time connections to a serial device
Emil Marone

Works very well and can save you lots of time connecting to serial devices for the first time. Lets you know if you need a null converter quickly

Works fine.
A D Haworth

Small and rugged. Shows line activity for trouble shooting RS-232 data lines in the field. Met my needs for testing.

Perfect for current nine pin RS-232 testing
Bonkers Bill

These were once hard to find - glad to have them here at Amazon. There are far too many 25 pin RS-232 testers on the market for a connector that's nearly disappeared. I have one of these in every tool kit and at every desk because they are indispensable for figuring out what's going on when a new piece of equipment wanders into the shop. [Update December 2013] One of the low-star reviews mentioned that these won't connect to chassis mount connectors that have jack sockets. I commented "Easy, unscrew the jack sockets on the tester". I got three new testers today and did that and the metal shells fell off. Older testers had captive metal shells so you could just unscrew the jack sockets if they get in the way. Today's don't. Four 4-40 screws will take care of it holding the shells on, but the product has changed in an unfortunate way.

RS232 is still alive
John Berry

People don't realize that many sensors and I/O devices still use serial connections. These are great for testing a connection and data flow.

Excellent - It does what it says it will do

I like some other reviewers know for a fact that serial connectivity is not dead, finding a tester for DB-9 is not off-the shelf available for sure and finding this on Amazon was a blessing. I was in need of a test unit that was inline and simple to use and understand for checking signals from a control panel to an RS-232 external control port to mounted video projectors. I have to ascertain when a projector does not turn on or off from the wall controller if it is the wall controller / wiring, or the projector - if I call the wrong vendor responsible for warranty / repair I have to eat the service call cost. Having a small test unit with a visual indicator makes the diagnosis very simple. I did not find the LED indictors "dim" as some others have mentioned, mine were nice and bright, and exhibited no "bleed over" to the LED next to it. This unit is rugged and does what it says it will do, I did find like some other reviewers that the nuts next to one side of the connector get in the way when not mating to a cable but directly a device, simple to remove however and not a problem at all. I would recommend this to others.

want a way to ensure your (CONNECTED) this is it

does the deed keeps me honest in the field when setting up gear and using *customers* wires on site. (S)


I use this on Arduino projects to detect which lines have the data on them. I wish I had bought one of these years ago.

9 Pin Serial "Tester" - RS-232 LED link Tester DB-9 Male to DB-9 Female

Good for "seeing" your serial traffic and connectivity. Small and compact. Well built. LEDs light up when the pins are active and flash when traffic is passing.

DB-9 Tester

Works very well, glad to have it. The female-thread retainers were cumbersome and interfered with some cables; I had to remove them with pliers. Also would have preferred lights to shine red for positive, green for negative, but it's ok this way too. Very handy item.

RS-232 DB-9 LED link tester
Bob S

The light for each line shows either none (dim), green, or red. I am not sure whether green means high, and red low, or something else. It works very well for loopback tests (TX connected to RX). It can only be inserted between two cables, not between a cable and a chassis.

Great little lamp box.

I first used this device when I was commissioning data centers for Clearwire. Our job was to start up a newly built data center. Most network equipment is initially configured via a serial connection. Most adhere to the "Cisco standard" but some are just down right odd. One of our tasks was to connect each device to a terminal server. That meant that we had to figure out each pin-out. This little matchbox sized lamp box saved our arses. If your life involves connecting to various odd serial ports, you want this. If you have a serial cable in your kit, you want this in there with it.

Excellent tester.

Though devices using serial connectivity are becoming a thing of the past, there are still a good number of devices that are not available with native USB connectivity and require serial port connectivity. Unfortunately, serial devices are not as plug-and-play as USB devices and thus often require some level of troubleshooting to get them up and working. This handy little link tester can be invaluable in determining if the serial connection is mated properly and if communications is occurring. I have used a number of these types of devices over the years and this particular 9-pin device is very convenient. The only drawback is the LEDs are not as bright as I would like to see. If you are in a brightly lit room or out of doors, it may be difficult to see the indication. Overall, I give this tester a thumbs-up.

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