In Singapore, most hotels require that guests be at least 18 years old to check in and stay alone in a room. This age requirement is in place to ensure the safety and security of guests, as well as to comply with local laws and regulations. Moreover, some hotels may require that guests under the age of 21 provide additional documentation or proof of permission from a parent or legal guardian before checking in. Therefore, if you are planning on staying alone in a hotel in Singapore, it is best to check with the specific hotel you plan to stay in to confirm their age requirements and policies.