I tried Sound Guard with a pair of UE 900s Noise Cancelling Earphones and my pair of molded custom UE In-Ear Reference, Capitol Records Edition. In both cases, it worked well at controlling the maximum level applied to these in-ear monitors. Sound Guard will work fine on any set of balance armature-style in-ears.

For on-the-body personal use, Sound Guard has a removable belt clip and runs on two, 3-volt CR2450 lithium batteries (included). It also comes with a short TRS-to-TRS patch cable to connect it to your in-ear receiver. Controls are simple: on and off with a green (battery is good) and red (operational) indicator LEDs. The device also functions as an audio buffer amp that matches the feed from the FOH, monitor mixer or receiver output to the correct impedance of the connected in-ear monitors.

I found using it causes the overall in-ear sound to take on a more consistent level--nothing was peaking with the more subtle elements of the in-ear mix brought up in level. I found I could hear more deeply into the mix as if I cranked the volume way up but without the worry of getting blasted.