Underwater Pressure Sensor?

I was wondering if there was a underwater depth/pressure sensor attachable to the Ardunio? For example if I reach 30 feet underwater the pressure sensor will tell an LED or vibrate motor to activate.

You can always make a sensor connecting to an Arduino as its 0..5V interface is quite generic and you can always add some level converter etc.
10 meters ==> pressure is ~2 ATM = 2 bar = 2.,026 hpa = 29.4 psi

To find a sensor for 30 feet (10 mtrs) should not be too hard ,
e.g. - http://www.digikey.com/product-detail/en/P51-200-G-B-I36-4.5V-000-000/734-1008-ND/1665769 -
(has a build in amplifier)

Q: what accuracy do you need? (#digits)

Is there one any cheaper? And I have no idea about the accuracy. I'm new at all this. My overall plan is to record data while scuba diving. So the components need to be small and compact.

don't now if there are cheaper ones, probably there are - try ebay -
be aware that the Arduino should be in a real watertight case if it is used underwater.

I've been working with the MS5803 series for underwater deployments:

But they are pretty expensive. If you could find the hoperf sensors, they run around $5 each. I have not found any US distributors though, and my emails direct to HopeRF keep resulting in a "1000 is our minimum order quantity" type responses.

@EKMallon
You could contact Terry King (also on this forum) , he has contacts in China and might be able to help you.
see also - YourDuino -

That would require an absolute pressure sensor and one rated for water/saltwater environment in it's sensor port, so not likely to be cheap. Most of the cheap hobby type pressure sensors are rated for dry air service only, so check the datasheet carefully before purchasing.

Lefty

I did not find any listings the HopeRF sensors at the yourduino.com sunshop. But I finally convinced Hope to send me 6 of the HSF1000-TQ sensors, which came to $50 with shipping. They did not have any of the 7 bar HSF0700-TQ to send, as they are special order only, so these sensors probably will not have the sensitivity I need.
Anyway, I will test them out and report back if & how they work (which will take a while). I will be sealing them under a protective cover of Qsil silicone, so they won't contact the water directly.

Also: it looks like I might be able to read the HSF1000 pressure sensors:
http://www.hoperf.com/upload/sensor/hsf1000-tq.pdf

with this HX711 Weighing Sensor Dual-Channel 24 Bit Precision A/D Module:
Sunrom Electronics (these boards are dirt cheap on ebay)

But I am new at this, so any advice is appreciated.

please can someone explain me how the pressure sensors work or it algorithm !!!

You have not specified a sensor, what are you wanting to do?