Mobile and Internet-of-Things (IoT) systems have been widely used in many aspects

of human’s life. These systems are storing and operating on more and more sensitive

data of users. Attackers may want to obtain the data to peek at users’ privacy or

pollute the data to cause system malfunction. In addition, these systems are not

user-friendly for some people such as children, senior citizens, and visually impaired

users. Therefore, it is of cardinal significance to improve both security and usability

of mobile and IoT systems. This report consists of four parts: one automatic locking

system for mobile devices, one systematic study of security issues in crowdsourced

indoor positioning systems, one usable indoor navigation system, and practical attacks

on home alarm IoT systems.

Chapter 1 overviews the challenges and existing solutions in these areas. Chapater

2 introduces a novel system ilock which can automatically and immediately lock the

mobile devices to prevent data theft. Chapter 3 proposes attacks and countermeasures

for crowdsourced indoor positioning systems. Chapter 4 presents a context-aware indoor

navigation system which is more user-friendly for visual impaired people. Chapter

5 investigates some novel attacks on commercial home alarm systems. Chapter 6

concludes the report and discuss the future work.