You can place an indoor thermometer anywhere in your home and it is advisable to keep one in a bedroom, bathroom, living room or any room where you need to monitor the temperature and humidity. There are, however, some places you should avoid placing a thermometer and they include:
Any spot in direct sunlight
Near a heat source such as vents or radiators
Near appliances that generate a lot of heat
On an external wall as you will get the outside temperature affecting the readings