It is a wireless heart rate monitor composed of an analogue chest strap transmitter and a wrist watch receiver.
It is water resistant up to 30m.
Summary
You can see that this heart rate monitor is VERY basic. It does not have a heart rate zone to warn you from overtraining or undertraining in an exercise session. It does not tell you the maximum heart rate you managed to reach during your exercise. It does not have a backlight. It does not even tell the time!
But it does the job if you are the kind of person who considers every feature (apart from showing the heart rate, of course) as an unwelcome distraction. If you are this type of person, then this is the perfect monitor for you!
Next one up in the Polar A series is the Polar A3. It represents a major improvement over the A1.
Note: This monitor is now discontinued i.e. Polar no longer makes it. The current entry level model is the Polar FS1 which corresponds most closely to the Polar A1.