Scaling notifications beyond alerts: from subtly drawing attention up to forcing the user to take action

New computational devices, in particular wearable devices, offer the unique property of always being available and thus to be able to constantly update the user with information, such as by notifications. While research has been done in sophisticated notifications, devices today mainly stick to a binary level of information, while they are either attention drawing or silent. In this paper, we want to go further and propose scalable notifications, which adjust the intensity reaching from subtle to obtrusive and even going beyond that level, while forcing the user to take action. To illustrate the technical feasibility and validity of this concept, we developed three prototypes providing mechano-pressure, thermal, and electrical feedback and evaluated them in different lab studies. Our first prototype provides subtle poking through to high and frequent pressure on the user's spine, which creates a significantly improved back posture. In a second scenario, the users are enabled to perceive the overuse of a drill by an increased temperature on the palm of a hand until the heat is intolerable and the users are forced to eventually put down the tool. The last project comprises a speed control in a driving simulation, while electric muscle stimulation on the users' legs conveys information on changing the car's speed by a perceived tingling until the system independently forces the foot to move. Although our selected scenarios are long way from being realistic, we see these lab studies as a means to validate our proof-of-concept. In conclusion, all studies' findings support the feasibility of our concept of a scalable notification system, including the system of forced intervention. While we envisage the implementation of our proof-of-concept into future wearables, more realistic application scenarios are worthy of exploration.