I tried one a few years back, that I bought on Amazon. The sensor clipped on to my diaper, and had a buzzer/vibrator unit that clipped onto my night shirt, near my collar. I had it set to vibrate only, to not wake the wife.
It worked every time, vibrating when wetness formed in my cloth diaper. But since I'm a deep sleeper, I usually didn't wake up right away. So I still had a moderately wet diaper by the time I awakened, then got up, changed my diaper, then tried to get back to sleep.....
After about 2 weeks of this, I thought "What am I gaining??" With the alarm, I was waking up, with a wet diaper, and loosing sleep during the whole process. Without the alarm, I was waking up with a wetter diaper, at my normal time, but getting a better nights' rest. Also, my wife was getting irritated that I was waking her up too, when I was getting up in the middle of the night to change. When I told her I was thinking of stop using the alarm, she said "Good, we can both get more sleep, and reduce your diaper laundry too!"