How to silence a noisy Laptop and Smartphones with a simple device key

Electronic devices seem to have an uncanny ability to
make noise at the worst possible times. It's always
during an important meeting, a quiet study session
at the library, or a biology final that your laptop or
smartphone decides to play some obnoxious or
embarrassing sound.
It goes without saying that muting a device would
prevent this problem, but if you forget to do so
before shutting down or entering sleep mode, it can
be difficult (if not impossible) to silence it before the
startup sound plays.
This is such a common annoyance that there's
currently a Kickstarter project for a muting device for
the iPhone. It plugs into the headphone jack to
silence all the sounds (alarms, apps, Siri) that can
play even when the iPhone is set to silent.
While buying such a product is pretty obviously
overkill, it begs the question: why don't
manufacturers just include a freaking mute button
on their devices?
To get around this unnecessary annoyance, computer
scientist Philip Peter made a simple hardware "mute
button" that attaches to his keyring. It was made
with a laptop in mind, but it'll work with any device
you can plug headphones into. All it takes is a 3.5
mm stereo jack and a little piece of insulated wire.
Using an audio jack as a silencer is hardly a new idea,
but adding a loop for your keychain means you'll
always know where it is, and never forget to bring it
with you. But, if you don't have a soldering iron to
attach the wire, it'll work just fine without it.
Philip also added a resistor, which "could provide
some fun additional uses and would also allow any
static to dissipate safely," but it's entirely optional.
This may not be the prettiest solution, but it works,
and it's a great way to get some use out of a broken
or crappy pair of headphones. Check out Philip's blog
for more details on how to make your own.
Alternatively, if you don't want to cut up a pair of
headphones, you can get the same results by using a
cheap Y-adapter cable or stereo jack adapter.