## 2 Materials and Methods
### Methodology
#### 2.2.2 Theoretical Model and Hypotheses  
The conceptual TAM consists of six constructs (Figure 2): (1) perceived usefulness, (2) perceived ease of use, (3) perceived playfulness, (4) attitude to use, (5) intention to use, and (6) perceived risk. In addition, these constructs are related to eight hypotheses. Details of these constructs and hypotheses are presented next. 1. Perceived Usefulness and Perceived Ease of Use  
Perceived usefulness means that when users use this new technology or new device, they can feel that it provides obvious help for their life, work, or learning and can improve their efficiency. In the preliminary study of the TAM, perceived usefulness and perceived ease of use are the most common and essential determinants of technology acceptance [32]. Perceived usefulness is usually defined as a person's belief that using a system will help improve their performance. Perceived ease of use is whether the user has operational difficulties and convenience when using this technology [33]. In this study, the perceived usefulness is redefined as whether the driver can effectively help alleviate driver fatigue and ensure the driver's safety when using the VP-ADD. The perceived ease of use is  
Figure 2: Conceptual model. defined as whether the driver can quickly operate this new technology, which will not increase the precious time of driving and will not bring more driving burden to the driver during driving. 2. Perceived Playfulness  
The VP-ADD is a new device that overturns the perception that traditional car per-fume can only last for a short amount of time. People may have a greater interest in it. Furthermore, it is very playable because it has many functions and can interact with the cell phone app in real time. Its presence will entertain the driver during the driving process and, therefore, they will be more willing to use it. 3. Attitude to Use and Intention to Use  
Accepting something new depends heavily on one's attitude, directly affecting one's willingness to use it. [PERSON] (2018) defines the attitude toward a new system as \"an individual's overall emotional response to using the system.\" [PERSON] et al. defined the behavioral intention to use the system as \"the degree to which an individual believes he or she will continue to use the system\" [PERSON] et al. (2018). Furthermore, the more favorable a person's attitude toward using a new system, the greater their intention to use it ([PERSON] et al., 2018). In this study, attitude to use and intention to use was defined as the driver's friendliness toward the VP-ADD. That is, whether they would be willing to try using the device and continue to use it in the future and recommend it to others around them. 4. Perceived Risk  
The importance of risk as a critical predictor of human behavior is undeniable. Perceived risk is a person's perception of whether he/she decides to perform an action or activity ([PERSON] et al., 2018). When users use any new technology or newly developed product, they consider the possible risks associated with its use. Perceived risk was negatively correlated with intention to use ([PERSON] et al., 2018). The higher the perceived risk, the lower the user's willingness to continue using it. During driving, drivers need to consider whether the device we have developed will pose a hidden risk to everyday driving, threaten the driver's life to some extent, or affect the typical driving environment. 5. Research Hypotheses  
Various factors usually influence a behavior or the acceptance of technology. Based on the above analysis, it is clear that perceived usefulness and ease of use, perceived playfulness, attitude to use, and perceived risk affect the willingness to use the devices we invent. To better explain this behavior, we developed a hypothetical model using an extended TAM. Based on the analysis of several variables, the following seven hypotheses were formulated (Figure 2). 1. _The perceived playfulness has a positive effect on perceived usefulness._
2.