<s>
It	O
is	O
a	O
type	O
of	O
wearable	B-Operating_System
computer	I-Operating_System
.	O
</s>
<s>
The	O
term	O
is	O
now	O
primarily	O
used	O
for	O
smartwatches	B-Application
that	O
are	O
synced	B-Application
,	O
in	O
many	O
cases	O
wirelessly	O
,	O
to	O
a	O
computer	O
or	O
smartphone	B-Application
for	O
long-term	O
data	O
tracking	O
.	O
</s>
<s>
There	O
are	O
also	O
independent	O
mobile	B-Application
and	O
Facebook	O
apps	O
.	O
</s>
<s>
The	O
term	O
"	O
activity	O
trackers	O
"	O
now	O
primarily	O
refers	O
to	O
wearable	B-Operating_System
devices	O
that	O
monitor	O
and	O
record	O
a	O
person	O
's	O
fitness	O
activity	O
.	O
</s>
<s>
Wearable	B-Operating_System
heart	O
rate	O
monitors	O
for	O
athletes	O
were	O
available	O
in	O
1981	O
.	O
</s>
<s>
Wearable	B-Operating_System
fitness	O
tracking	O
devices	O
,	O
including	O
wireless	O
heart	O
rate	O
monitoring	O
that	O
integrated	O
with	O
commercial-grade	O
fitness	O
equipment	O
found	O
in	O
gyms	O
,	O
were	O
available	O
in	O
consumer-grade	O
electronics	O
by	O
at	O
least	O
the	O
early	O
2000s	O
.	O
</s>
<s>
Early	O
versions	O
such	O
as	O
the	O
original	O
Fitbit	B-Application
(	O
2009	O
)	O
,	O
were	O
worn	O
clipped	O
to	O
the	O
waist	O
;	O
formats	O
have	O
since	O
diversified	O
to	O
include	O
wristbands	O
and	O
armbands	O
(	O
smart	B-Device
bands	I-Device
)	O
and	O
smaller	O
devices	O
that	O
can	O
be	O
clipped	O
wherever	O
preferred	O
.	O
</s>
<s>
Apple	O
and	O
Nike	O
together	O
developed	O
the	O
Nike+iPod	B-Application
,	O
a	O
sensor-equipped	O
shoe	O
that	O
worked	O
with	O
an	O
iPod	B-Device
Nano	I-Device
.	O
</s>
<s>
In	O
addition	O
,	O
logging	O
apps	O
exist	O
for	O
smartphones	B-Application
and	O
Facebook	O
;	O
the	O
Nike+	B-Application
system	O
now	O
works	O
without	O
the	O
shoe	O
sensor	O
,	O
through	O
the	O
GPS	O
unit	O
in	O
the	O
phone	O
.	O
</s>
<s>
The	O
Apple	B-Device
Watch	I-Device
and	O
some	O
other	O
smart	B-Application
watches	I-Application
offer	O
fitness	O
tracker	O
functions	O
.	O
</s>
<s>
In	O
the	O
US	O
,	O
BodyMedia	B-Device
has	O
developed	O
a	O
disposable	O
activity	O
tracker	O
to	O
be	O
worn	O
for	O
a	O
week	O
,	O
which	O
is	O
aimed	O
at	O
medical	O
and	O
insurance	O
providers	O
and	O
employers	O
seeking	O
to	O
measure	O
employees	O
 '	O
fitness	O
,	O
and	O
Jawbone	O
's	O
UP	O
for	O
Groups	O
aggregates	O
and	O
anonymizes	O
data	O
from	O
the	O
company	O
's	O
wearable	B-Operating_System
activity	O
trackers	O
and	O
apps	O
for	O
employers	O
.	O
</s>
<s>
Earbuds	O
and	O
headphones	B-Device
are	O
a	O
better	O
location	O
for	O
measuring	O
some	O
data	O
,	O
including	O
core	O
body	O
temperature	O
;	O
Valencell	B-Device
has	O
developed	O
sensor	O
technology	O
for	O
new	O
activity	O
trackers	O
that	O
take	O
their	O
readings	O
at	O
the	O
ear	O
rather	O
than	O
the	O
wrist	O
,	O
arm	O
,	O
or	O
waist	O
.	O
</s>
<s>
The	O
standard	O
activity-tracking	O
smartphone	B-Application
or	O
web	O
apps	O
present	O
data	O
in	O
statistical	O
form	O
meant	O
to	O
be	O
viewed	O
after	O
the	O
activity	O
has	O
ended	O
.	O
</s>
<s>
Wearable	B-Operating_System
sensors	O
have	O
been	O
widely	O
used	O
in	O
medical	O
sciences	O
,	O
sports	O
and	O
security	O
.	O
</s>
<s>
Wearable	B-Operating_System
sensors	O
can	O
detect	O
abnormal	O
and	O
unforeseen	O
situations	O
,	O
and	O
monitor	O
physiological	O
parameters	O
and	O
symptoms	O
through	O
these	O
trackers	O
.	O
</s>
<s>
Moreover	O
,	O
in	O
sports	O
training	O
there	O
is	O
an	O
increasing	O
demand	O
for	O
wearable	B-Operating_System
sensors	O
.	O
</s>
<s>
For	O
example	O
,	O
measurement	O
of	O
sweat	O
rate	O
was	O
possible	O
only	O
in	O
laboratory	O
based	O
systems	O
a	O
few	O
years	O
ago	O
,	O
but	O
is	O
now	O
possible	O
using	O
wearable	B-Operating_System
sensors	O
.	O
</s>
<s>
However	O
,	O
the	O
results	O
of	O
a	O
study	O
among	O
semi-professional	O
(	O
half	O
-	O
)	O
marathon	B-Application
participants	O
suggests	O
that	O
these	O
users	O
are	O
open	O
towards	O
sharing	O
tracked	O
activity	O
data	O
on	O
a	O
voluntary	O
basis	O
with	O
:	O
friends	O
(	O
51.7	O
%	O
)	O
,	O
family	O
members	O
(	O
43.4	O
%	O
)	O
,	O
or	O
a	O
physician	O
(	O
32.3	O
%	O
)	O
.	O
</s>
