How do you open a sealed envelope without it being noticable?

consider lightly rubbing the envelope with 100% acetone. This makes the envelope virtually see-thru before evaporating and returning the envelope to its normal appearance... works quite well with unfolded letters. **Test your acetone for lingering smell before using it on the envelope of intrest**.  more

This is going to be pretty hard to explain but I'll give it a go. Get a thin piece of dowel and cut a slit down the length of it. Push the dowel into the envelope in the top corner under the flap. Now manipulate the letter through the envelope so that the edge of it sits in the slit in the dowel once you have it secure spin the dowel in your fingers so the letter wraps around it, then pull your stolen letter and piece of dowel out of the envelope. This all depends on the sender leaving a gap under the flap sufficient for your dowel and writing the coveted letter on paper thin enough to be rolled. Stealing mail is a federal offence.  more

In addition to the other answers, there is a way of reading the contents of an envelope without opening it. It requires either a light table used for tracing things or a very sunny day. Simply hold up the envelop to the light and you will most likely be able to read what its written/printed on the paper. Of course, the more papers there are layered together the more confusing it will be (because the print will overlap) or it won't allow enough light through to read anything. But this way the envelop is unharmed and you've read the contents (and if the words are backwards, flip the envelop over). P.S. Before someone comments, I know this doesn't answer the question of how to open it, I'm just offering and alternative that will in many instances still allow you to see some of the contents of the envelop (which would be the reason a person would want to open an envelop in the first place).  more