The market for voice assistants (VAs) and other allied voice-based smart-home products is gradually emerging. The initial growth has been slower than expected; therefore, an in-depth simultaneous intention and diffusion analysis is needed for identifying the relevant factors along with finding out the target consumers. This work uses technology acceptance model as the core for analyzing the adoption intention of the VA-based system and extends it with three additional factors: compatibility, perceived complementarity and privacy concerns. The diffusion analysis for the same is done using the multivariate probit model. Certain characteristics of the VA-based systems like the network effects between the products/services and the importance of protecting personal information are considered in this work, apart from various demographic variables like age, gender, income and education levels. Two separate surveys were conducted for the purpose of data collection from 315 and 1945 participants residing in Thailand for analyzing the adoption and diffusion scenario, respectively. The results show that usefulness, ease of use, compatibility and perceived complementarity have significant positive effects on the purchase intention. In terms of diffusion of the VA market, unlike other Information Communication Technology-based products/services, the results show that the senior consumers are more likely to purchase the VAs and other allied smart-home devices within a given time frame when compared to the younger consumers. Therefore, new strategies should be developed that promote the usage of VAs by the young population for increasing the market demand.