I chose the DHT11 / DHT22 sensor because it reads a couple values and uses digital logic. The small ESP-01 module only has two digital pins free (GPIO0 and GPIO2). No analog pin is available so using a TMP36 sensor is out.
So what other digital sensors would also work:
Changing up the Internet interface, using the Twitter APIs to tweet when a sensor is activated is possible (I have not tried if the ESP will do an SSL connection which can be hard). Sending readings to Adafruit.io would be great also. It is all up to you.