Have you found a weather balloon?

Launched from the ground, radiosondes are meteorological devices that are used to measure temperature, humidity, pressure, wind speed and direction in the upper atmosphere. A balloon filled with hydrogen or helium gas carries the radiosonde into the upper atmosphere. Depending on the size of the balloon, the expansion that takes place as it rises into lower pressure causes the balloon to burst and the instrument will fall back to Earth to where you found it in this case. During the radiosonde’s flight, it constantly transmits atmospheric temperature, humidity and pressure data to automated receiving ground equipment. This equipment, called a sounding system, processes and converts the data into meteorological weather messages that are sent to the global weather network.

Radiosondes are launched by our various customers such as the national weather institutes, environmental and research organizations. Unfortunately, we do not keep a record of what serial number goes to what customer so we don't know who has sent those individual radiosondes that land on the ground.
 
Should you have found a radiosonde, and there are instructions on the radiosonde cover for returning the device, please follow them. If there are no instructions for returning the device and you do not want to keep it, please dispose of it by following your country’s guidelines for the disposal of electrical waste. If you want to keep the radiosonde, please remove the battery and dispose of it in an approved receptacle for used batteries.

The Vaisala Radiosonde you have found poses no danger to you. It is also made of materials that are benign in the natural environment.