When you receive the detectors (3 in a carton) and connect the provided 9V battery, it will operate as expected sounding a loud alarm when a leak is detected. I am happy with the purchase and would certainly recommend it. However that said, the device can be mechanically improved. Permit me to explain.When you remove the detector from the first of three plastic bags, you need to open the back cover in order to insert the battery. Here is the first challenge since it is not clear how to open it (and the meager instructions do not address this). As you'll note from one of the photos, two "tabs" at one end of the unit when closed, fit into the slots. Thus to open the back, use a small flat-head screwdriver and push the tabs down so that they clear the slots. It's not easy the first time but thereafter it's not too bad and besides, you need to do this only when replacing the 9V battery (hopefully infrequently).Once the back cover is opened, you'll immediately note the small plastic bag containing two small screws. So it seems the manufacturer may be suggesting to use the two screws if A) you wish to have an additional closure mechanism (can't imagine why), or B) if the tabs break off, using the screws in place of the tabs. I certainly did not use the screws and in fact, used a small file to try and reduce the size of the tabs so that the cover would open easier.And by now you must have noticed the suction cup on the back cover used to attach the device to a surface. For me, the suction cup didn't work. Although the manufacturer provides a double-sided tape, this too is not a good solution since the tape will need to be ripped away whenever replacing the battery. A much better solution would be a piece of velcro on the back cover, or a "3M Company Re-Close Strip" (similar to the EZPASS attachment used on a car windshield), or gluing a small magnet to the back cover (thereby enabling attachment to a metal surface). With any of these options, the device can easily be removed and replaced without destroying the attachment itself.So now that the back cover is open, the 9V battery can be connected, leading to another small challenge (as many have previously noted). The battery compartment is very tight making it difficult to place the connected battery into the compartment. However here's what worked for me. First connect the battery to the associated snaps. Second, ensure that the battery cable will be situated at the bottom of the compartment (not the top) when inserting the battery. Third, using your fingers reduce the width of the battery snaps as much as possible so that it's about the same width as the battery itself. Fourth, insert the battery into the compartment with the snaps end first and then press down on the other end to push it into the compartment. After you've done so once or twice, it becomes relatively easy. (Of course, had the manufacturer increased the case width by only an 1/8 inch, this would not be an issue.)Having inserted the battery, the back cover needs to be closed, an easy operation, and the probe needs to be attached to the base (or platform), also an easy operation. At this point, I'd suggest you test the unit. To do so, simply moisten your index finger and for an instant slightly touch the probe. If should emits a loud shrill sound, indicating that the unit is functioning correctly. The device is now ready to be placed into operation, to the area where you wish to detect a water leak.Now should you be interested and have the time, here are a couple of improvements I've made. They are not essential to the operation but I believe it will make the device more reliable and sensitive.1st improvement: Because the probe and base assembly is so light weight, it may easily move around a bit and thus no longer lie flat on the surface, essential for optimum operation. To get around the light weight of the base base, you can glue on some material on either side of the base, such as screw nuts or as I used, dead AAA batteries (see photo). Thus by making the base heavier, once placed on the surface to be monitored, it will lie flat and not have the tendency to move around as easily.2nd improvement: This improvement, actually suggested by other users (thank you) is in the sensitivity of the detector. The plastic of the base to which the probe is attached is about 1/32 inch in thickness. Therefore the detector will detect water accumulation only when it reaches about 1/32 inch. By placing a tissue that's been rolled and crunched up into the bottom center channel of the base (see photo), the first indication of water will be wicked up by the tissue and thus activate the audible alarm much sooner than if the water had to accumulate to 1/32 inch in height. However just be careful that the tissue lies totally flat to the base.In summary, this is a very worthwhile and economical water leak detector. The mechanical issues described above should not detract you from purchasing the device. And once familiarized, these challenges become less of an issue the next time you deal with it. Finally it's important to note that the device relies heavily on the condition of the battery. It's prudent to check the battery condition on a regular basis, and possibly to replace it with a fresh one annually (or sooner if deemed necessary). Using masking tape or similar, I mark the date I last changed the battery on the case.Good luck.... hope this helps.Having recently received a 2nd order of units, this package cam along with a very reasonably sized and readable Instruction Manual (see photo). Evidently the manufacturer must be reading our comments...good! The most important part of this manual addresses the LOW BATTERY ALERT which reads as follows: "When the battery is low and needs to be replaced, you will hear an interval "beep" sound. Please replace battery with a new one." That said, I think it would still be wise to replace the battery annually.