Step 1: Recall what magnetic effect of current means.
It refers to a current producing a magnetic field, which can then be used to attract iron, run a motor, or induce another current.
Step 2: Check each device against that idea.
An electric bell uses an electromagnet to pull a striker, a motor uses a magnetic field to push a current carrying coil into rotation, and a generator uses a changing magnetic field to induce current, all three rely on magnetism.
Step 3: Look at the heater separately.
A heater simply pushes current through a high resistance wire, and the electrons colliding with the atoms of that wire release heat directly, no magnetic field plays any role in producing that heat.
\[ \boxed{\text{Electric heater}} \]