The Heat Sensors Law is now in effect, which mandates the city’s Department of Housing Preservation and Development to select 50 buildings with the most heat violations for the installation of heat sensors.

Landlords of the selected buildings are required to pay for and install the devices. One company, Heat Seek, charges $69.99 for each sensor and $7.99 a month for the app.

MORE: Heat Sensors Program

The law, written by Bronx Councilman Ritchie Torres, allows for the recording of temperature along with the date and time of the reading to ensure tenants are getting the proper amount of heat.

The information is accessible to property owners and tenants.

"A heat sensor allows HPD to monitor minute-by-minute changes in heat and hot water levels without depending on a upon an inspector, so we are bringing housing code enforcement into the 21st century," said Torres.

The councilman says another part of the legislation includes biweekly inspections in the worst buildings regardless of whether tenants submit a complaint to 311.