Typically sensors are built into a mobile device and there are many applications of the sensor with a good interface. However, using those sensors require special programming or something that we all have “a phone app”. These are now almost all complete and so there is probably an app for whatever you need even if it is not free.
A company now has integrated a sensor with all kinds of cloud based computing so that something gets triggered depending on what the sensor reads. This is a simple wifi based sensor (simple as in free to use rather than pay the wireless bills). It comes prebuilt with a wifi, and can sense humidity, orientation or even presence of water.
Check out its numerous uses on the companies website.