I recently purchased three of these smoke alarms from Amazon. Can you tell me how high up on the wall the alarm should be installed as I do not want to install on ceiling. I specifically purchased these as they can be ceiling or wall mounted. Thanks.

The instructions that come with the unit duplicate what I have read from several Fire Department sources: you can place your unit on the ceiling, but AT LEAST 4 inches (10cm) from the wall. If you want to mount it on the wall, mount it MORE THAN 4 inches (10cm) BELOW the ceiling, but NO LOWER than12 inches (30cm) below the ceiling. It has to be high enough up the wall to "smell" the smoke, but that 4 x 4 inch (10cm x 10cm) area where the wall meets the ceiling can sometimes harbor a "dead zone" of still air where the smoke would NOT reach the detector quickly enough during a fire to warn you in time. Thus, do NOT mount your detectors too close to where the wall meets the ceiling.

Is this detector a photoelectric or ionization type?

Please check with your local authority having jurisdiction. Also you can check with NFPA online. Ionization smoke alarms are generally more responsive to flaming fires. How they work: Ionization-type smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm. Download this chart on ionization smoke alarms (PDF, 943 KB). Photoelectric smoke alarms are generally more responsive to fires that begin with a long period of smoldering (called “smoldering fires”). How they work: Photoelectric-type alarms aim a light source into a sensing chamber at an angle away from the sensor. Smoke enters the chamber, reflecting light onto the light sensor; triggering the alarm. Download this chart on photoelectric smoke alarms (PDF, 782 KB).

Does the unit beep to tell you that the battery is running low?

The beep is effective. It always seems to start in the middle of the night. I twist the unit off the ceiling and do a battery swap and have it back on the ceiling in less than a minute, craw back into bed before really waking up. It's not a pain to replace the batteries, it's very easy. Simply slide the tray out and pop new ones in. The batteries fit snuggly in the compartment and there are tabs that allow you to push the batteries out by applying pressure with your thumbs from the back side. There is an optional screw hole to make the battery compartment tamper resistant. This prevents people from easily taking the batteries to power their remote controls or whatever. When fire marshals inspect fire related deaths it's not uncommon to find the smoke and fire detectors had no batteries installed. This simple, optional, screw might seem like "a pain" to some people, but it's an easy way to save your life. This is a great unit. I have 6 in my house and I highly recommend them to everyone.

Brand	First Alert
Style	Compact
Power Source	Battery Powered
Colour	White
Item Weight	0.7 Pounds
Alarm	Audible
Sensor Type	Photoelectric
Global Trade Identification Number	00029054015358
Manufacturer	Jarden Safety
UPC	029054015358
Item model number	SA320FF
Product Dimensions	12.7 x 12.7 x 5.08 cm; 317.51 g
ASIN	B00O8MVW0S

First Alert SA320CN Dual Sensor Battery-Powered Smoke and Fire Alarm

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