: Spontaneous interaction in public places has evolved as crucial concern in interaction design, particularly in the domain of public advertising. Implicit interaction is a mode of spontaneous interaction in which the user is not attentively or explicitly expressing input to a system, but the system from observing the user, and considering all the available information that describes the user situation, is used to generate input - and behaves accordingly. We have investigated implicit interaction as a potentially effective means to design for spontaneous interaction in the public. An en passant coupon collection system, CCS, has been developed to implement an implicit interaction based pervasive advertisement process. CCS is based on scanning and identifying Wi-Fi hotspots by their BSSID, and has been implemented for internet enabled smart phones. Scenarios demonstrate how the system collects bonus points, rewards, sales coupons, reward coins, etc. by users just walking by points of in...