article. Huge Australian study says cell phones haven’t increased brain cancer rates, after all

http://qz.com/677772/huge-australian-study-says-cell-phones-havent-increased-brain-cancer-rates-after-all/

but wait until 2023, the association with Cell Phones high/intensive usage and gliomas, meningiomas, or acoustic neuromas risks will be clear. 
It will quite similar as the 20 years lag between smoking and lung cancer development.
Glioma is a broad category of brain and spinal cord tumors that come from glial cells, the main brain cells that can develop into tumors. The only risk factor for malignant gliomas is prior radiation to the brain. Family history accounts for less than 5% of causes for developing these tumors. Some genetic disorders increase the risk of development of these tumors in children but rarely in adults.

Mobile phones ARE linked to cancer, study claims: Long-term use 'is associated with Alzheimer's, Parkinson's, headaches and skin irritation'

•     Radiation from wireless devices such as phones and tablets could be linked to a number of health risks, a new review of studies has claimed
•     Scientists claim radiation causes oxidative stress in the body - a damaging process thought to be closely linked to degenerative diseases
•     Study authors say mobile phone use should be minimised to prevent harm
•     Official guidelines state the devices could 'possibly' cause cancer

 http://www.dailymail.co.uk/health/article-3181406/Mobile-phones-linked-cancer-scientist-claims-Long-term-use-causes-disease-headaches-skin-irritation.html

As for wearable, remember Wi Fi is microwave radiation.
Please see the paper: LONG-TERM EXPOSURE TO MICROWAVE RADIATION PROVOKES CANCER GROWTH: EVIDENCES FROM RADARS AND MOBILE COMMUNICATION SYSTEMS.
http://onlinedatingsoundbarrier.blogspot.com.ar/2014/05/long-term-exposure-to-microwave.html