The quantified self movement aims to provide us with the tools and techniques to collect and analyse data about the way we live, so we can take action to improve ourselves. As the devices we use to track ourselves become more mainstream, are we considering the impact that this vast collection of data has on the privacy of those around us?

There are many devices out there to help collect data on ourselves. From wearable pedometers, heart rate trackers and sleep monitors, to smart scales, air quality samplers and the ubiquitous smart phone.

What is that thing?

People don’t know why you would want to collect data about yourself or record so many aspects of your life. It can be seen as geeky, or slightly creepy. The motives behind the quantified self movement are not yet widely understood.

Many people don’t recognise wearable personal tracking devices yet. When they do, they often have concerns over what the device can and can’t record. The headline-grabbing devices such as Google Glass are often paired with media attention to their privacy implications. So what are the risks with the collection of this data?

As data collection devices proliferate then it becomes easier to get a full picture of your life. Data collection is now automatic and not tied to a specific action such as a check-in. It’s always on.

Some see mobile tracking devices and apps as a form of participatory surveillance. You can decide to track and share your data with friends, clinicians, insurers, or a network of like-minded people.

“Is it recording me too?”

However, collecting data on yourself also collects data on others by proxy.

If you know what I have had for a meal then you likely know what the person I live with has had for a meal.When I share a bed with my partner, tracking my sleep tracks an approximation of their sleep.

As data is aggregated it will be easier to interpolate the lives of others.

Out of my data, we will be able to build a picture of your data too.

But, you did not consent to your data being tracked.

What responsibility do I have to you? What responsibility do we have as device and software developers to respect non-users privacy?

We are already feeling the effects of this data collection and sharing. Pity those people who told their partners they were having a quiet night out, but whose friends checked in at the pub and recorded a vast number of beers on Untapped.

Facebook has recently been criticised for a bug that revealed the shadow profiles of over six million of its users. This included users private emails and phone numbers, none of which they had consented to share. It is obvious that Facebook collects far more information than this on users from their friends, even when the user themselves does not use the site regularly.

Looking forward to the future, there is the prospect of insurance companies customising coverage based on self-reported data of you and your peers. Marketing companies predicting your preferences from those of your friends, supplementing the data they already collect on your buying habits.

Governments could now establish your political preference and monitor your activity based on data from the people you interact with. In light of the recent revelations of many countries putting large numbers of their own citizens under the dragnet of surveillance we have to ask: are our data-collecting peers participating in surveillance on our behalf?

What rights do we have to demand that our data not be collated by our peers, companies and Government?

These devices and apps are an exciting step in the quantified self movement, but we must remember that when designing these devices it isn’t just a single user that will be recorded - and consenting to being recorded - but all the people that person interacts with too.