I have been told that there is some use of handwarmers and people who
use them for avoidance or mis-reads on drug tests. If correct I am
looking for how this is accomplished. Or, just what is the connection
between handwarmers and drugs, or drug testing. (I found a number of
handwarmmers in my sons car, and the logic or use is unclear. in
seching the internet I found some indication that there is a
connection between the handwaremer and drugs.)

The connection between handwarmers and drug tests is a relatively
simple one and involves no real groundbreaking science.

If a person is required to take a urine drugs test they usually need
to supply a fresh sample and as we all know fresh urine is warm.  The
commonest way for cheats to pass these tests therefore is to warm a
bag of cold urine up using a handwarmer.

They obtain the urine from someone they know has not taken any drugs
for the past few weeks or months and carry a small sample of this with
them at all times.  When they are required to pass urine for a drugs
test, they warm the small bag up on a handwarmer and fill the test jar
with the warmed urine.  Handwarmers are used because they heat up
instantly and are easy to conceal about your person.  They are often
used in treatments of injuries so can be carried legitimately without
any real suspicion.

There is even a commercial product that helps you evade the drugs tests:
http://www.thewhizzinator.com/whiz3.htm

A quick note about this usage is documented here:
http://www.marijuana.com/420/archive/index.php/t-30143.html

Further methods of evasion that are known to the authorities and
rarely work can be found here:
http://www.passyourdrugtest.com/Employee-Drug-Tests-Accurate.htm

I do not condone the use of any of these products and hopefully
because they are well known that no official drugs tester will be
fooled by such a simple trick.  I also hope your suspicions are
unfounded and that your son is not taking any form of illegal drugs.

If you have any further questions regarding this please ask for
clarification and I will do all I can to help.

Perhaps you could talk to your son instead of searching his possessions.

Are you really helping him?

Maybe he has cold hands... daytrader76 is right, it is much better to
just talk to children if you suspect them of using drugs. There are
few things worse for a child than being presented with a list of
'evidence' collected from personal possessions, hysterical articles in
newspapers and from the internet. If he is using drugs then he will
not turn to you for advice because trust has been  undermined... and
if he isn't he will think you're nuts and paranoid. Trust is far more
important than anything else in these situations...